Every asset in your plan follows a set of simulation rules. This page describes how each asset type behaves month by month, so you know what the engine will do with the numbers you give it.
The simulator tracks your home’s market value month by month, growing it at the annual rate you set (or shrinking it, if the rate is negative). When you sell, it works out the tax on the gain.
Rule 1Your home's value compounds monthly so that a full year appreciates by exactly the annual return rate — 3% means 3%, giving you a realistic appreciation curve over time.
Rule 2Property tax is calculated using the annual tax rate you set, deducted monthly, and tracked as a separate expense metric so you can see exactly where your money goes.
Rule 3Carrying costs — maintenance (a percentage of the home’s value) and insurance (a fixed annual cost) — are charged monthly to the funding account set in the home’s fund transfers. If none is set, the funding backstop pays them (see Fund Transfers).
Rule 4When you sell, the gain is measured against your cost basis, and the primary-residence exclusion is applied automatically if the home has been held more than 24 months. Those months count from the home’s start date in the plan, so a home entered at the plan’s first month is treated as newly bought (see What This Engine Does Not Model). The exclusion follows your filing status: $250,000 filing Single, $500,000 filing jointly. Unlike most figures in the tax tables it is never indexed for inflation: IRC §121 has not changed it since 1997, so a long-held home is less sheltered the further out you project.
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Mortgage
A full amortization schedule. Enter your remaining balance, rate and months left (from your statement), and the simulator builds the payment plan to the penny.
Rule 1Monthly payments are calculated using the standard amortization formula, splitting each payment into principal and interest so you can watch your equity grow. The rate is an APR: each month charges 1/12 of it on the balance, exactly as your lender does.
Rule 2The simulator tracks your months remaining and automatically closes the mortgage when the balance reaches zero — no manual cleanup needed. This works even if no finish date is set; the mortgage closes implicitly when fully amortized.
Rule 3Mortgage interest is tracked as a deductible expense, giving you visibility into one of your largest annual tax write-offs.
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Working Income
Your salary drives the plan. It is credited on the first of the month with withholding taken out, so what reaches your accounts is your take-home pay.
Rule 1Your gross income is credited on day 1 of each month. At year-end the full annual return rate is applied once as a raise — unlike balances and expenses, which compound a little every month, a salary steps up once a year the way a real one does.
Rule 2FICA and Medicare are withheld automatically from each paycheck, so fund transfers downstream reflect your actual net income — not your gross.
Rule 3Federal income tax withholding is estimated from your filing status and tax bracket, as a payroll department would.
Rule 4A paycheck pays out only what it earns, in payroll's order: FICA, then income tax withholding, then pre-tax 401(k) and IRA deferrals from what is left, then your take-home pay. In a month whose withholding estimate is larger than the paycheck — the month a 401(k) is cashed out, say — the paycheck withholds all it can and the monthly true-up collects the rest from your funding accounts. A deferral the paycheck cannot cover is cut, and the rest of the year's limit stays available to later paychecks.
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Monthly Expense
Bills don’t stay flat. Expenses grow with inflation, so you can test whether your plan holds up over 10, 20 or 30 years.
Rule 1Expenses are debited at the end of each month, after all income and transfers have settled — mirroring how bills work in real life.
Rule 2Starting from month two, inflation is applied at the beginning of each month, compounding so that a full year rises by exactly the annual rate — your $500 grocery bill today won't be $500 in a decade.
Rule 3Salary rises once a year; expenses rise a little every month. Over a full year both reach their annual rate — the difference is only in when the increase arrives.
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Retirement Accounts
401(k) · IRA · Roth
Whether you defer tax now, pay it later or never pay it, the simulator enforces the IRS contribution limits and withdrawal rules.
Rule 1Annual contribution limits are enforced against a household total. Filing Single: $24,500 for 401(k) ($32,500 if 50+) and $7,500 for IRA/Roth ($8,600 if 50+). Filing jointly, each figure is doubled — $49,000 and $65,000 for 401(k), $15,000 and $17,200 for IRA/Roth. Limits start from the 2026 figures and are indexed forward by your inflation rate each simulated year. Contributions are sourced from linked income via fund transfers; anything over the cap stays in the source account and is reported as a Contribution capped note.
Rule 2Required Minimum Distributions follow SECURE Act 2.0 rules: age 72 if born before 1951, age 73 if born 1951–1959, age 75 if born 1960 or later. The simulator uses the IRS Uniform Lifetime Table to calculate your annual RMD automatically.
Rule 3Tax treatment follows real-world rules: 401(k) and IRA withdrawals are taxed as ordinary income, while Roth distributions are tax-free — a powerful lever in your retirement planning.
Rule 410% federal tax is withheld at the source of every traditional IRA or 401(k) distribution, mirroring the custodian default when no election is filed. The draw is grossed up, so a $1,000 transfer still delivers $1,000 and an extra $111 leaves the account as withholding. Roth is excluded — the test is whether the account is tax-deferred, not whether it is a retirement account. If the account is empty, the withholding is re-sourced from your funding accounts; it is never skipped.
Rule 5Withholding governs where the cash comes from, not what you owe. The monthly and annual true-ups reconcile over- and under-withholding in both directions, so the household's total tax is the same either way — and a refund is credited back rather than dropped. Only tax an account actually paid counts as withheld: what your funding accounts cannot cover is flagged as unfunded, and the year is settled against what was paid.
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Taxable Account (Brokerage)
Your taxable investment account. The simulator tracks your cost basis, so the gain on each withdrawal is measured and taxed correctly.
Rule 1Growth compounds monthly so that a full year earns exactly the annual return rate — the way a market return is measured, so 8.5% means 8.5%. Your cost basis is tracked separately, so gains are always measured against what you actually invested.
Rule 2On withdrawal, basis is reduced proportionally — not dollar-for-dollar — so your realized gain reflects the correct share of appreciation.
Rule 3Gains realized by withdrawals are taxed at long-term capital-gains rates. Short-term rates apply only when the whole account closes within 12 months of its start date (see What This Engine Does Not Model).
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Cash
In your wallet, your checking account, or under the mattress. Cash is king for liquidity — but unless you're in a deflationary spiral, it's your worst-performing asset class over time.
Rule 1If you assign an annual return rate, interest accrues monthly and is treated as ordinary income for tax purposes.
Rule 2No cost basis is tracked — every dollar withdrawn is a dollar, making cash the simplest asset type in the simulator.
Rule 3Cash is the first account the funding backstop draws on, and where leftover take-home pay and sale proceeds land when no fund transfer says otherwise.
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Savings
High-yield savings accounts and certificates of deposit. A safe harbor for your emergency fund or short-term goals, with predictable returns and no market risk.
Rule 1Interest accrues monthly so that a full year earns exactly the annual rate, like a savings APY, and is classified as ordinary income.
Rule 2Behaves identically to cash in terms of tax treatment, but gives you a dedicated card to model different rates for different buckets of safe money.
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Debt
Credit cards, auto loans, student debt — anything with a balance and a rate. You set the payoff timeline, and the simulator builds the amortization schedule around it.
Rule 1Uses the same amortization formula as a mortgage, splitting each payment into principal and interest based on your rate and payoff period.
Rule 2You control the months-to-payoff — want to see what happens if you pay off that credit card in 12 months instead of 36? Change one number.
Rule 3Once the balance reaches zero, interest stops accruing — the debt stays open (like a line of credit at $0) but doesn't generate reverse interest. Mortgages automatically close when fully amortized.
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US Treasury
Bills, notes, and bonds backed by the full faith and credit of the United States government. The benchmark for risk-free returns — and a cornerstone of conservative portfolios.
Rule 1Interest income accrues monthly via the annual return rate and is taxed as ordinary income at the federal level.
Rule 2The principal value stays flat — no price appreciation or depreciation is modeled, keeping the simulation focused on coupon income.
Rule 3Interest income flows into your annual tax computation, so you can see how treasuries affect your overall bracket and liability.
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Corporate Bond
Higher coupons, higher risk. Corporate bonds let you model the yield premium you earn for lending to companies instead of the government — and the simulator treats the income accordingly.
Rule 1Interest accrues monthly so that a full year earns exactly the annual rate, just like treasuries — but typically at a higher coupon to reflect credit risk.
Rule 2All coupon income is taxed as ordinary income — no preferential capital gains treatment here.
Rule 3Like treasuries, no price appreciation is modeled — the focus is on predictable income, not speculative gains.
Fund Transfers
Fund transfers move a percentage of one asset’s value into another on a schedule you control: salary into a 401(k), a brokerage account into cash, or a one-time sweep when an asset closes.
Recurring Transfers
Set a monthly percentage of the source asset's value to move each month into the target account.
On-Close Transfers
When an asset reaches its finish date, a separate close percentage sweeps the remaining value into the target account automatically.
System Transfers
Mortgage payments, property tax, maintenance, insurance and tax settlements are automatically debited from your funding accounts. These implicit flows appear in the Flows view under Moved automatically, beside your configured transfers.
Funding Backstop
When no transfer you configured covers an obligation, the engine falls back to your everyday accounts in a fixed order — Cash → Savings → Taxable Account → US Treasury → Corporate Bond — and the first one holding a positive balance pays. Retirement accounts are never chosen automatically at any age: spending a 401(k), IRA or Roth has tax and penalty consequences the simulator will not decide for you. If nothing is eligible, the payment is recorded as Unfunded rather than quietly skipped.
Where the Money Went
Switch to the Flows view in Your Portfolio to see what actually moved in a month or a year: one bar per source of money, its parts into your accounts, spent, or paid in tax. Under the bars, each rule in force sits beside what it moved, and the money no rule sent is listed as automatic.
Rebalance Engine
Capital-to-capital, capital-to-retirement, and retirement-to-capital transfers run on day 1 of each month after the payroll pipeline completes. This means salary deposits and 401(k) contributions are settled before rebalancing pulls from accounts. Roth conversions, early mortgage payoff, and savings → brokerage sweeps all route through here, with realized gains picked up automatically by the monthly tax true-up.
Metrics
Every asset tracks a rich set of metrics each month — balances, flows, taxes, and returns. Four of them are pinned so they always appear first wherever you cycle metrics (timeline, projections, visualizer, asset cards).
💰 Net Worth
The balance at the end of the month. Added up across your assets it is your net worth, which is how it is labelled in the metric menus and badges.
📊 Net Worth Change (derived)
The change in Net Worth from one month to the next. It combines growth and cash flow in one number, so you can see when spending is outpacing growth.
📈 Growth
Appreciation earned through the annual return rate, compounded monthly so that a full year earns exactly that rate. Does not include deposits or withdrawals — pure market return.
💸 Cash Flow
Income received from outside your accounts — wages, Social Security, pensions, interest and dividends — less expenses (living costs, the whole mortgage payment, maintenance and insurance) and every tax booked. A withdrawal from one of your own accounts, or a transfer between them, is not cash flow. Added up across your accounts it is the household’s cash flow in Reports and in Month & Year Details. In retirement it usually runs negative: that is what your savings covered.
Why track Net Worth Change? Growth alone is misleading during retirement — a portfolio can grow 6% while withdrawals drain 8%, leaving you poorer. Net Worth Change is the honest bottom line: did my wealth actually go up or down this month?
Tax Rates
Every run starts from the 2026 federal tables for your filing status: income brackets, capital-gains bands, the standard deduction, the Social Security wage base and the retirement contribution limits. From age 65 the standard deduction grows by the additional deduction for age 65 or older ($2,050 single, $1,650 per spouse in 2026), and for tax years 2025 through 2028 the senior deduction adds $6,000 per person on top, phasing out at 6% of income over $75,000 / $150,000. A household that itemizes keeps the senior deduction but not the additional standard deduction.
From the second simulated year onward, all of those figures are indexed forward by your inflation rate — brackets widen, the deduction rises, the wage base climbs. That keeps a 30-year projection from quietly pushing you into the top bracket through inflation alone. Some figures are deliberately held fixed, because Congress never indexed them: the primary-home sale exclusion at $250,000 / $500,000, the Net Investment Income Tax threshold at $200,000 / $250,000, the Social Security provisional-income thresholds, and the senior deduction. The thresholds catch more households every year by standing still, and a simulator that quietly inflated them would model a tax that fades away. Here are the publications we reference:
An extra 3.8% on investment income, charged once a year on top of ordinary and capital-gains tax. It applies to the lesser of two numbers, which is why a large gain does not automatically mean a large surcharge:
Your net investment income
Interest, dividends of both kinds, and capital gains both short and long. Wages, Social Security, pensions and withdrawals from retirement accounts are not investment income and are never taxed by it.
How far you are over the threshold
$200,000 filing single, $250,000 filing jointly, measured against your adjusted gross income — before the standard deduction, not after. Under the threshold, nothing is due however much of your income is investment income.
⚠️ The part worth planning around
A withdrawal or Roth conversion from an IRA or 401(k) can never be taxed by this surcharge — but it does raise your adjusted gross income, and by doing so it can drag your investment income over the threshold. So a large conversion can trigger 3.8% on gains and dividends you were not otherwise going to be surcharged on. Roth distributions raise neither number and are safe on both counts. If you are sizing a conversion, this is often the constraint that binds first.
The simulator charges it once a year, with the annual tax true-up; real life has no withholding for it either. You will find it in the Taxes column of Your Portfolio, in Reports and as its own line in the Spreadsheet. Because it is paid after the year ends, a yearly report shows it under Prior-Year Settlement, the year after the income it taxes; the adjusted gross income it was measured against is in the previous year’s report.
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ACA Health Insurance
IRC §36B · Premium Tax Credit
An ACA Health Insurance card is a marketplace plan’s premium, with the premium tax credit worked out the way Form 8962 does it. It answers how much is the subsidy under the transfers you already have; it never changes which accounts pay.
Rule 1Each month the credit is the benchmark premium (the second-lowest-cost silver plan for your household) less your expected contribution, never more than the premium itself. Your contribution is a percentage of your ACA MAGI: AGI plus the Social Security that is not taxed. The percentage rises with income, from 2.10% to 9.96% of it in 2026 and 2.15% to 10.22% in 2027.
Rule 2The credit needs household income from 100% to 400% of the poverty line for your household’s size, which comes from your filing status unless the card names one. One dollar over 400% loses all of it: the enhanced credits that removed the cliff expired after 2025. In 2027 the cliff is $63,840 for one person and $86,560 for two. Under 100% there is no credit, unless the advance was paid on an estimate of 100% or more.
Rule 3The credit is advanced each month on an estimate of the year’s income: last year’s ACA MAGI when you had the plan all of last year, otherwise the card’s Estimated Income. With neither, nothing is advanced. Advance Credit % takes less in advance, as some early retirees do to lower the risk of repaying.
Rule 4The year is settled on the return, booked the following January like the tax true-up: excess advance is repaid in full, with no cap from 2026, and credit still owed is paid to you. A plan that starts after January cannot see the year’s earlier months, so its first year is settled against the card’s estimate.
Rule 5Marketplace plans are priced by calendar year, so the premium and benchmark step once a year, in January, at the card’s growth rate. It defaults to inflation and is usually well above it; in a backtest the card keeps that excess on top of the year’s CPI. Past 2027 the poverty line is indexed like the tax tables, and the percentages move with the card’s growth over inflation, as the law adjusts them for premiums rising faster than incomes.
Rule 6Coverage ends at Medicare: a card with no finish date ends the December before you turn 65.
The premium and the advance are lines in the card’s Expenses group in Month & Year Details, and the tax-year strip shows the credit the year allowed. The January settlement is in the Taxes column, under Prior-Year Settlement in Reports, and in each yearly report’s credit rows.
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Filing Status
Single · Married Filing Jointly
Set Filing As in the Settings Row at the top of the page and the whole tax model moves with it. Filing jointly is not a discount applied at the end — it selects a different table at every point where tax is computed.
What changes
Income brackets, capital gains bands, the standard deduction, the primary-home sale exclusion, and the 401(k) and IRA contribution allowances all switch to their joint figures.
Household, not per-person
The simulation models one household, not two individuals. Contribution limits are enforced against a household total, so a married plan gets two 401(k) allowances between all its income assets — not one each, tracked separately.
Two incomes, one plan
Model a second earner by adding a second Working Income asset. The joint Quick Start profiles do exactly this — Salary A and Salary B, each with its own rate and retirement date.
Quick Start follows your status
The welcome banner offers the four profiles that match your filing status — Early Career, Mid Career, Pre-Retirement and Retired for Single; Young Couple, Dual Income Couple, Couple Nearing Retirement and Retired Couple for joint filers.
Known limitThe Social Security wage base is shared across a married household rather than granted per spouse. Two high earners who would each get their own cap therefore stop paying Social Security tax earlier than they really would, overstating take-home pay. This bites only when combined wages clear the cap; everything else about joint filing is modelled per the tables.
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Retirement Income
Social Security · Annuities
The income that kicks in when the paychecks stop. Model Social Security benefits or any recurring income stream that starts at a future date — so your retirement projections don't pretend you're living on air.
Rule 1Income is credited monthly starting on the asset's start date — perfect for modeling a Social Security benefit that begins at 62, 67, or 70. Social Security can’t begin before 62, the earliest the law allows a claim: a benefit dated earlier starts in January of the year you turn 62, at the amount entered, and What needs attention says so. Quick Start, the Retirement Age setting and the asset form never date one earlier.
Rule 2An optional annual return rate applies cost-of-living adjustments (COLA) at year-end, so your benefit keeps pace with inflation over a 30-year retirement.
Rule 3Retirement income is taxed as ordinary income but is exempt from FICA and Medicare — a benefit is not wages.
Rule 4Social Security withholds nothing by default, and that is a modelling choice rather than an omission. Form W-4V is elective — most recipients never file one — so withholding by default would model a decision your household never made. The tax is still owed; it is settled from your funding accounts at the monthly and annual true-ups.
Rule 5Social Security is taxed by the IRS provisional-income test: your other income plus half your benefits. Below $25,000 single / $32,000 joint none of the benefit is taxable; up to $34,000 / $44,000 at most half of it is; above that at most 85%. Capital gains count toward provisional income. The thresholds have never been indexed, so a growing share of benefits becomes taxable in later decades.
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Pension
FERS · CSRS · Military · State/Local
Model defined-benefit pension payments separately from Social Security. Pensions have their own COLA schedule, and they are taxed differently: a pension is fully taxable income, while only part of a Social Security benefit is (see Rule 5).
Rule 1Monthly pension income is credited starting on the asset's start date, just like Retirement Income.
Rule 2The annual return rate applies COLA adjustments (e.g. FERS 2% cap) — separate from Social Security COLA.
Rule 3Pension income is taxed as ordinary income but is exempt from FICA. No contributions or RMDs apply.
Rule 410% federal tax is withheld on arrival, standing in for the Form W-4P default of withholding on periodic payments unless you elect otherwise. A pension is a flow with no balance to debit, so the withholding reduces what it pays out — the deposits you see are net of tax. The year-end true-up refunds any excess.
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Life Events & Phases
Your financial life isn't one long straight line — it's a series of phases. During accumulation, your salary flows into 401(k)s and brokerage accounts. In retirement, the flow reverses: Social Security and retirement account drawdowns fund your living expenses. Life Events capture these transitions and automatically rewire your portfolio when each phase begins.
🟢 Accumulate Phase
The earning years. Income flows into savings, investments, and retirement accounts. Fund transfers route your salary to 401(k), Roth IRA, and brokerage based on the percentages you set for this phase.
🟠 Retire Phase
The drawdown years. Salary closes automatically. Social Security begins, or at 62 if you retire before then. Fund transfers flip: retirement accounts and brokerage now fund your living expenses — all configured independently from the accumulation phase.
Phase TransfersEach life event owns its own set of fund transfers. When you configure "Salary → 5% to 401(k)" in Accumulate and "401(k) → 40% to Living Expenses" in Retire, the simulator automatically switches between them at the transition age you set.
Asset ClosingLife events can close assets when a phase begins. When Retire triggers, Salary automatically closes — its on-close transfers fire, and the asset stops producing income. No manual intervention needed.
Color-Coded TimelineThe timeline shows each phase as a colored band — green for Accumulate, coral for Retire. Click a phase’s chip, or its dot on the axis, to edit it.
Age-DrivenPhases are triggered by age, not fixed dates. On a new plan they follow the Current Age, Retirement Age and Finish Age in the settings row. On a loaded plan, changing Retirement Age moves the Retire phase together with the salary end and benefit start dates tied to it, and Finish Age sets the plan’s last year.
Why it mattersWithout phases, you'd need separate portfolios for "working" and "retired." Life Events let you model your entire financial arc — from first paycheck to last withdrawal — in a single simulation, with fund transfers that adapt to each chapter of your life.
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Why It Did That
A number you can't explain is a number you can't trust. Two surfaces report what the rules on this page actually did to your plan — one for the plan as a whole, one for a single asset. Both are derived from events the engine recorded while running, never recomputed afterwards, so what they say is what happened.
⚠️ What needs attention
A panel above your asset list, grouped into 💸 Paying for the plan and 🔧 Needs setting up. It catches the month the plan runs out of money, obligations nothing could pay, accounts that ran dry and were covered by the next one down, contributions that hit the annual limit, and required distributions that were not met.
📖 Rule notes on an asset
Open any asset’s 👓 view to read its metrics over this month, this year and life to date, with plain-language notes on the rules that fired: why a Roth paid no tax, where the tax on untaxed income was settled, what was withheld from a pension, why a contribution was capped.
Depletion is not an alarmA retiree's accounts are supposed to draw down — that is the scenario being modelled, not a fault. Nothing fires on a zero balance alone. The ⚠️ on a card means an obligation that could not be paid, which is a different and much rarer thing.
Silence is the contractA false “you could not pay your mortgage” is worse than saying nothing at all. Every check is built to stay quiet unless the engine actually recorded the failure it is describing.
Engine diagnosticsA third category, 🧪 Engine diagnostics, reports where the simulation's own bookkeeping does not reconcile. It is hidden unless you enable it in Globals — those are notes about the engine, not about your finances.
What This Engine Does Not Model
Knowing where a model stops is part of reading it. These are deliberate, verified gaps — each one makes your projection optimistic or pessimistic in a specific, nameable direction.
No early-withdrawal penalty
The 10% additional tax on distributions before age 59½ is not charged, and the engine has no concept of that age. A plan that retires early and draws a 401(k) or IRA will look better than it would be. Optimistic.
No state or local income tax
Federal only. Property tax is modelled; state income tax, local tax and state-specific retirement-income exemptions are not. Optimistic in most states.
A married household has one age
Age-based rules — the deductions from 65, catch-up contribution limits and RMDs — treat both spouses as the age you enter. A couple where only one is 65 or older gets both spouses’ age deductions here. Optimistic for couples with an age gap.
A home’s holding period starts in the plan
The 24 months the primary-residence exclusion needs are counted from the home’s start date in the plan, not from when you bought it. A home you have owned for years, entered at the plan’s first month and sold within two years, is taxed without the exclusion. Pessimistic.
Withdrawals are always long-term
Gains realized by withdrawing from a taxable account are taxed at long-term rates however recently the money went in. Short-term rates apply only when an account closes within 12 months of its start. Optimistic for recent purchases.
One Social Security wage base per household
Married filers share a single cap instead of one each, so two high earners stop paying Social Security tax earlier than they would. Optimistic above the cap.
No rental income
Rent is net investment income, and an income property is not a supported asset type yet — real estate here is a residence. A landlord's Net Investment Income Tax will be understated until that asset exists. Optimistic for property investors.
Investment expenses are not deducted
Net investment income is counted gross. Advisory fees, investment interest and the state tax allocable to that income would all reduce it in a real return, and none is tracked here. Slightly pessimistic.
No RMD penalty
A required minimum distribution that goes unmet is reported in “What needs attention”, but the excise tax a real shortfall would incur is not charged. Optimistic.
No Medicaid or state help with premiums
Under 100% of the poverty line a health-insurance card gets no premium tax credit, and Medicaid, which covers adults under 138% in most states, is not modelled; nor are state subsidies or the cost-sharing reductions that lower deductibles. Pessimistic for low incomes.
Premiums are not age-rated
A marketplace premium rises at the card’s one growth rate. Real premiums also rise with age, roughly tripling between 21 and 64, and the benchmark with them. Optimistic unless the rate allows for it.
No self-employed health insurance deduction
A self-employed household can deduct its premiums above the line, which lowers ACA MAGI and raises the credit. Neither the deduction nor its interplay with the credit is modelled. Pessimistic for the self-employed.
Projections & Analysis
A single projection is a starting point, not the whole story. The simulator offers several ways to test your plan, from the deterministic projection to Monte Carlo simulation and an optimizer.
📈 Projections
Your deterministic projection: stacked bar charts of any metric, asset by asset, month by month, for the whole plan.
🎲 Monte Carlo
1,000 stochastic simulations with percentile bands. See below for the full story.
🛡️ Guardrails
Dynamic withdrawal rules that adapt spending to market reality. Details below.
📋 Spreadsheet
A detailed monthly data table across all metrics and assets — for when you want the raw numbers, not the chart.
🧾 Credit Memos
A complete record of every transaction — every credit, debit and transfer, with its date and a note describing it.
📊 30+ Metrics
Track value, growth, income, dividends, capital gains, taxes, RMDs, contributions, distributions, cash flow, and more.
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Monte Carlo Simulation
Your financial plan doesn't live in a world of fixed returns — so why should your projections? Monte Carlo simulation runs your portfolio through 1,000 randomized trials, each drawing from real historical market data, to show you the range of outcomes your plan might actually produce.
Correlated Year Sampling
Each trial picks a single historical year for all asset classes — S&P 500, treasury yields, CPI, and wage growth move together, preserving the real-world correlations that matter.
Percentile Bands
Results are summarized as 10th, 25th, 50th, 75th, and 90th percentile envelopes, with your deterministic baseline overlaid — so you can see the best case, the worst case, and everything in between.
Optional Guardrails
Check “With Guardrails” to apply your guardrail rules in all 1,000 simulations and see how adaptive spending changes the range of outcomes.
Calibrated or Historical
Each trial draws years from FRED data for 1970–2025 (or from your backtest year on). Calibrated, the default, keeps your own return and inflation rates and adds each drawn year’s swing around its long-run average. Historical uses the drawn years’ actual returns.
Always Current, Always Repeatable
The simulations re-run whenever the plan changes, and the draws are seeded, so the same plan always gives the same answer. When a result moves, it is because the plan did.
Why it mattersA single projection tells you what happens if everything goes exactly as planned. Monte Carlo tells you how likely that plan is to survive — and what to expect when it doesn't.
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Guyton-Klinger Guardrails
The 4% rule is a starting point, not a strategy. Guyton-Klinger guardrails adjust retirement spending as your portfolio moves: when your withdrawal rate drifts too high, spending is cut; when it drifts low, spending rises.
Target Rate
Your starting withdrawal as a percentage of the portfolio. The guardrails adjust spending from here.
Preservation Band
If your current withdrawal rate drifts above the initial rate by this margin, spending is cut — protecting your portfolio from depletion in down markets.
Prosperity Band
If your current withdrawal rate drifts below the initial rate by this margin, spending increases — so you actually enjoy the upside when markets deliver.
Adjustment Amount
The percentage by which withdrawals are raised or lowered when a guardrail is triggered — controlling how aggressively the system responds.
Dual-axis chartThe guardrails projection plots portfolio value and withdrawal amounts on separate axes, with event markers showing exactly when and why each adjustment fired.
Per-scenarioGuardrail parameters are saved per portfolio scenario, so you can compare conservative vs. aggressive withdrawal strategies side by side.
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Historical Backtesting
What if you could run your portfolio through actual market history? Backtesting replaces your user-provided rates with real historical data and advances year by year through the simulation — so you can see how your plan would have performed from any starting year between 1970 and 2025.
S&P 500 Annual Returns
Applied to equity accounts — Brokerage, 401(k), IRA, and Roth IRA — so your investments track actual market performance.
10-Year Treasury Rates
Applied to US Treasury bonds, reflecting the real yield environment for each historical year.
CPI Inflation
Applied to monthly expenses, so your cost of living grows at the actual inflation rate — not a static estimate.
Nominal Wage Growth
Applied to monthly income, so your salary tracks real historical wage growth year over year.
NoteHistorical data covers 1970–2025, sourced from FRED (Federal Reserve Economic Data). Once the simulation advances past the available historical years, your user-provided rates automatically resume for the remainder of the projection.
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Maximizer
Genetic Algorithm Optimizer
The Maximizer searches for the fund transfer percentages and guardrail settings that best serve your goal. It uses a genetic algorithm, modelled on natural selection, and runs inside the Maximizer section, updating the chart as it finds better solutions.
Spending ↔ Terminal Value Selector
A row of discrete notches lets you set the optimization objective. All the way left maximizes lifetime cash flow (spending in retirement). All the way right maximizes ending portfolio value (wealth preservation). Pick any point in between for a blended goal.
Evolvable Guardrail Genes
The optimizer doesn't just tune fund transfers — it also evolves your guardrail parameters (withdrawal rate, preservation, prosperity, adjustment) within realistic ranges to find the sweet spot for your chosen objective.
Phase-Aware Optimization
The chromosome encodes fund transfers grouped by life event phase. Accumulate-phase allocations are evolved independently from retire-phase allocations, and only assets active during a phase are included — Social Security won't appear in accumulation genes.
Real-Time Chart Updates
Watch the portfolio projection chart update live as the optimizer discovers better solutions. The generation counter, fitness status, and best terminal value are displayed below the chart throughout the run.
Real-World Constraints
A truly useful optimizer can't just chase math — it has to respect reality. The Maximizer enforces three tiers of constraints so its recommendations are actionable, not theoretical.
🔒 Immutable Transfers
Real Estate, Mortgage, and Debt fund transfers are locked to their original values. You can't optimize away your mortgage payment — it's a contractual obligation.
🔏 Partially Mutable
Monthly Expenses can vary ±25% of their original allocation. You can tighten the belt, but you can't eliminate groceries.
✅ Fully Mutable
All other transfers (salary routing, retirement account contributions, Social Security allocation) can be freely optimized from 0% to 100%.
Contribution CapsDuring accumulation, no more than 25% of income can flow to retirement accounts (401(k), IRA, Roth). In retirement, the cap drops to 10%. This prevents the optimizer from producing unrealistic over-contributions.
Debt PenaltyAny individual asset that ends with a negative balance incurs a fitness penalty proportional to the debt. This prevents the optimizer from concentrating losses in one account while inflating others.
Volatility PenaltyPortfolios that trigger frequent preservation cuts (guardrail spending reductions) are penalized — because a plan that constantly slashes your income isn't really a plan.
Recommendations
When the optimizer finishes, click Recommendations to compare your current fund transfers and guardrail settings with the best solution found, phase by phase, with the change for every transfer. Apply to Baseline writes them into your plan.
How it worksA population of 50 candidate portfolios competes over 200 generations. Each candidate encodes fund transfer percentages for every phase plus four guardrail parameters. The fittest survive, crossover, and mutate — converging on an allocation that respects real-world constraints while maximizing your chosen objective. The entire process runs in a Web Worker so the UI stays responsive.
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AI Summaries
Every section of the simulator has a floating ⚡ button that generates a structured markdown summary of your portfolio's current state — ready to paste into a conversation with your financial advisor, an AI assistant, or your own notes. Each summary is tailored to its section and includes directional notes pointing to related insights elsewhere in the tool.
📅 Timeline Summary
Life event phases, trigger ages, fund transfer configurations per phase, and which assets close at each transition.
💼 Portfolio Summary
Every asset with starting value, ending value, asset type, annual return rate, and fund transfer routing.
📈 Projections Summary
Metric snapshots at key dates — start, retirement, and finish — with per-asset breakdowns and growth trends.
🎲 Monte Carlo Summary
Percentile ending values (10th through 90th), baseline comparison, and 10th–90th spread with warnings if the downside is negative.
🛡 Guardrails Summary
Current guardrail parameters and a table of every preservation cut or prosperity raise that fired during the simulation, with the year and adjusted rate.
📋 Details Summary
Credit memo audit totals per asset, lifetime tax summary (income, FICA, Medicare, capital gains, property), and annual cash flow table.
Why it mattersFinancial data is only useful if you can communicate it. Each summary is structured markdown — tables, headers, and bullet points — designed to be pasted into ChatGPT, Claude, an email to your advisor, or a planning document. Copy with one click.
Scenarios & Sharing
One plan is never enough. The simulator lets you build multiple scenarios — different retirement dates, different allocation strategies, different assumptions — and compare them instantly. When you're ready, share your entire portfolio with a single link.
Multiple Scenarios
Create scenarios with different assumptions — each with its own assets, fund transfers, life events, settings (ages, filing status, inflation, backtest year) and guardrail parameters — and switch between them from the scenario menu in the Timeline heading.
Instant Sharing
Share your plan as a link, by email or by copying it. The recipient opens your exact scenario — assets, transfers, settings and guardrails. Open shows it without storing anything, so their own scenarios stay as they were; Open & Save adds it as a new scenario, on its own settings.
Auto-Persistence
Every change is automatically saved to your browser's local storage. Close the tab, come back tomorrow — your portfolio is exactly where you left it.
Growth at a Glance
The timeline shows the plan’s opening and closing values, in nominal and today’s dollars, and each phase’s annual growth rate, or a dash where the phase does not start and end above $0.