What's modeled, what isn't
This is the reference page for how far to trust a projection. Every other page links back here. If you read one thing before putting your real numbers in, read this.
Its companion, Simplifications, takes the entries marked Simplified below and tells you which direction each one bends your result.
Accounts and assets
Section titled “Accounts and assets”| Status | Notes | |
|---|---|---|
| Taxable and brokerage accounts | Modeled | Cost basis tracked; gains taxed pro rata on sale |
| Traditional IRA and 401(k) | Modeled | Withdrawals taxed as ordinary income; RMDs applied |
| Roth IRA and Roth 401(k) | Modeled | Contributions come out first, tax free |
| Cash and savings | Modeled | Yield only, no appreciation |
| 529 college savings | Simplified | Spent on education first; education spending is assumed qualified |
| HSA | Simplified | Spent on healthcare first; all healthcare spending is assumed qualified |
| Real estate | Not modeled | Property values are not assets in the projection. See below |
| Vehicles and other property | Not modeled | Same reasoning as real estate |
| Annuities | Not modeled | Can be approximated as an income event |
| Pensions | Partly | Enter as income. Survivor elections and pension-specific rules are not modeled |
| Cryptocurrency, private equity, collectibles | Not modeled | No account type for them |
On real estate. This is a cash flow forecaster, not a net worth tracker. What decides whether your money lasts is the cash a thing produces or consumes, not what it would fetch if sold. A paid-off house produces no cash and consumes plenty, and counting it as an asset makes a plan look fundable when it is not.
What to do instead:
- Rental property: enter the net income under Income. It inflates like other amounts entered in today’s dollars, which is roughly how rents behave.
- A planned downsize or sale: a one-time income event in the year you would sell.
- A mortgage: a liability. It amortizes, and the payment is deducted from cash flow automatically.
If you own several properties, this is not the only tool you should be using.
The market
Section titled “The market”| Status | Notes | |
|---|---|---|
| Simulated returns from historical data | Modeled | 1,000 paths, US history 1928 to 2025 |
| Stocks, bonds, and cash as separate sleeves | Modeled | Broad US stock index, broad US bond index, money-market cash. What that means |
| Inflation | Modeled | Simulated per path, correlated with the rest |
| Sequence of returns risk | Modeled | The main thing the simulation exists to capture |
| Per-account allocation | Modeled | Every account holds its own stocks / bonds / cash mix and grows at the rate that mix earns, so where you hold something changes your returns and your tax |
| Rebalancing | Modeled | Two strategies. The default steers toward your target inside IRAs, 401(k)s and Roths, and in taxable accounts only as far as it adds no tax. Let it drift never trades to a mix; it is the comparison, not the recommendation. 529 and HSA accounts are never steered. How rebalancing works |
| Individual funds, expense ratios, advisory fees | Not modeled | No fee drag of any kind is applied |
| International vs domestic split | Not modeled | One stock sleeve |
| Bond duration or credit choices | Not modeled | One bond sleeve |
Covered in full on How taxes are estimated. In brief: 2026 federal and all-50-state tables, capital gains stacking, net investment income tax, payroll tax, taxable Social Security, and RMDs are modeled. Itemizing, local income tax, the AMT, most credits, QBI, Roth conversions, retirement-income exclusions outside the eight modeled states, and filing statuses other than Single and Married Filing Jointly are not. The personal exemption credit is modeled in Arkansas, California, Nebraska, and Oregon.
Withdrawals and account ordering
Section titled “Withdrawals and account ordering”| Status | Notes | |
|---|---|---|
| Spending and taxes solved together | Modeled | A withdrawal raises the tax, which raises the withdrawal |
| Drawdown order | Modeled | Taxable, then tax-deferred, then tax-free. An imported priority list cannot exclude an account class |
| Penalty-free money used first | Modeled | The order cannot pull penalized money ahead of clean money |
| Early withdrawal penalties | Modeled | 59½ for IRAs, 55 for workplace plans, 20% on a pre-65 HSA |
| Required minimum distributions | Modeled | SECURE 2.0 start ages, Uniform Lifetime Table |
| Drawdown order editor | Not built yet | The engine honors a sensible order; there is no UI to change it |
| Withdrawal strategy modes | Not modeled yet | No fixed-percentage or guardrails strategy |
| 72(t) / SEPP payments | Not modeled | An early retiree using one looks worse here than in life |
| Roth conversion ladders | Not modeled | Same |
| The Roth 5-year clock | Not modeled | |
| Hardship, first-home, disability exceptions | Not modeled | |
| Still-working 401(k) RMD delay | Not modeled |
Contributions and saving
Section titled “Contributions and saving”| Status | Notes | |
|---|---|---|
| Surplus routed to 401(k), then IRA, then taxable | Modeled | Using 2026 statutory limits |
| Catch-up contributions | Modeled | Including the higher band in the years you turn 60 to 63 |
| Deduction and Roth phase-outs | Modeled | |
| Spousal IRA | Modeled | Both spouses share one earned-income limit; the same earnings cannot back contributions twice |
| Employer match | Not modeled | A real omission for anyone still working |
| Backdoor and mega-backdoor Roth | Not modeled | |
| SIMPLE and SEP plans | Not modeled | |
| Contributions while drawing down | Not modeled | A plan selling assets to live makes no contributions |
Cash flow, debts, and timing
Section titled “Cash flow, debts, and timing”| Status | Notes | |
|---|---|---|
| Income and expense events | Modeled | Monthly, yearly, one-time, or every N years |
| Today’s dollars vs future dollars | Modeled | Per event |
| Credit cards, loans, mortgages | Modeled | Amortized monthly; payments deducted automatically |
| Partial first year | Modeled | Remaining whole months only |
| Month-level timing | Not modeled | Each year is one lump. Nothing compounds inside a year |
| Paycheck withholding | Not modeled | One payment per year. A partial first year takes only the remaining share, at full-year brackets |
| Milestones as first-class events | Not built yet | Timing uses years and ages instead |
Life events and spending categories
Section titled “Life events and spending categories”| Status | Notes | |
|---|---|---|
| Education spending and 529s | Simplified | All education spending assumed 529-qualified |
| Healthcare spending and HSAs | Simplified | All healthcare spending assumed HSA-qualified |
| Medicare premiums and IRMAA | Not modeled | Enter them as healthcare expenses |
| Healthcare inflation | Not modeled | Healthcare rises with general CPI, which is optimistic |
| Long-term care | Not modeled | Enter as a large late-life expense if you want to test it |
| Essential vs discretionary spending | Not built yet | All spending is treated as required |
| Divorce, disability, death of a spouse | Not modeled | Only as much as you can express in income and expense entries |
| Social Security claiming | Partial | Yearly amount and start age 62 to 70, checked against statutory min and max. One row per person; a second row for the same person is flagged so you can delete the extra from Income. After a Social Security edit, leaving Inputs may show an optional reminder to check spousal eligibility with SSA. It never requires adding or increasing benefits. Enter the total gross benefit, including any spousal supplement. Switching between benefit types over time is not modeled. Widow benefits from 60 are not modeled. |
Your data
Section titled “Your data”| Status | Notes | |
|---|---|---|
| Local storage in your browser | Yes | Nothing is sent to our servers unless you choose a feature that would. See Privacy |
| Accounts and sign-in | None | Not built, and never required for the forecaster |
| Cloud sync | Not built yet | If offered, it will be opt-in |
| Export and import | Yes | Settings › Your plans downloads a file of your plans and uploads one back. Nothing is sent to us. |
What to take from this
Section titled “What to take from this”The projection is a good model of a household whose wealth is in savings and investment accounts, whose spending is reasonably predictable, and who lives in the United States. It gets progressively rougher as your situation moves away from that: substantial rental property, an employer match you are counting on, a conversion ladder you plan to run, or long-term care as a real possibility.
Where your plan leans on something in the Not modeled column, treat the output as a sketch. Then read Simplifications to see which way it is likely to be wrong.