Guide
Will my money last in retirement?
A useful answer puts spending, income, taxes, and uncertain returns on one timeline, then shows which assumptions can change the result.
By Steven, Founder · Updated September 2, 2026
Short answer
- A useful answer combines a year-by-year projection with uncertainty tests, not one withdrawal rule.
- Spending, retirement length, return sequence, taxes, Social Security, and RMDs must share one timeline.
- Stress tests reveal which assumptions matter; the result remains an estimate, not a guarantee.
Start with spending and the years the plan must cover
A retirement projection starts with the spending your portfolio must fund and the number of years it may need to fund it. Separate recurring needs from flexible wants, include healthcare, and extend the plan beyond an average life expectancy so the answer does not depend on dying on schedule.
Then place each income source on the timeline. Wages may stop first, Social Security or a pension may begin later, and required minimum distributions can start later still. The portfolio funds the gap between those events.
Returns and their order both matter
The average return is not enough. Poor returns early in retirement can force withdrawals from a depressed portfolio, leaving less invested for a later recovery. The same average return in a different order can produce a different ending balance.
A Monte Carlo simulation runs the same plan across many market paths and reports how often the money remains available through the planning horizon. It quantifies the assumptions in the model; it does not predict markets or guarantee an outcome.
Calculate the answer after taxes
Traditional-account withdrawals, Roth withdrawals, and taxable-account sales do not produce the same spendable amount. Required minimum distributions can add ordinary income, and other income can change how much of a Social Security benefit is taxable.
A useful projection therefore calculates income, withdrawals, and federal tax in each year rather than applying one tax rate to the ending portfolio.
Stress-test the decisions you can change
Run the same plan with lower returns, higher inflation, a longer life, earlier bad markets, and higher spending. Then change one controllable assumption at a time: retirement date, spending, Social Security timing, or a planned Roth conversion.
The purpose is not to find one perfect forecast. It is to learn which assumptions can break the plan, which decisions create useful margin, and which results barely change when conditions move.
Know what the model leaves out
Any result is only as complete as its inputs and model. Meridary's current planner covers two-earner wages, one Social Security benefit and its taxation, federal tax plus a flat state rate, RMDs, Roth conversions, healthcare estimates, and simulated or historical return paths.
It does not model a house, mortgage, other debt, a Social Security survivor transition, every state tax rule, or every possible future law change. Those boundaries belong beside the result, not hidden behind it.
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Frequently asked
- What probability means my retirement plan is safe?
- There is no universal cutoff. A modeled probability depends on the return model, planning horizon, spending assumptions, and what counts as success. Compare scenarios and the assumptions behind them instead of treating one percentage as a guarantee.
- Is a Monte Carlo result a guarantee?
- No. It estimates how often a plan lasts across the market paths generated by that model. It makes uncertainty visible; it does not remove it.
Read next
Sources
- Retirement benefits — Social Security Administration
Social Security retirement eligibility, claiming, and benefit-estimate resources.
Accessed September 2, 2026
- Required minimum distributions — Internal Revenue Service
RMD starting rules, deadlines, account coverage, and calculation method.
Accessed September 2, 2026
- Publication 590-B (2025) — Internal Revenue Service
The Uniform Lifetime, Joint Life, and Single Life tables used for 2026 distributions.
Accessed September 2, 2026
This is an educational estimate, not tax or financial advice. Figures reflect the law year shown and the inputs you provide. Consult a qualified professional before acting.