A single growth rate assumes markets return the same amount every year. They don’t. This tool runs your 403(b) through hundreds of simulated market paths and reports how often you actually hit your retirement income target.
Free to run. Pro unlocks the year-by-year range chart and live what-if.
How to use it
Pick your state. It sets the pension tax rate used for the after-tax figure.
Enter what you know. Final average salary, years of service and your plan’s multiplier come from your annual pension statement; the 403(b) balance from your provider.
Set the horizon. Years until retirement, plus what you contribute monthly and how fast that rises.
Read the odds, not the number. A single balance is one guess. The success rate tells you how often that plan worked across hundreds of market histories.
Do not have a pension? Set the multiplier to 0 and the tool projects the 403(b) alone.
Your outcome
Chance of hitting target
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Median ending balance
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the middle outcome across all paths
Median monthly income
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Range of outcomes, year by year
10th–90th percentileMedian
Pessimistic (p10)
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Median (p50)
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Optimistic (p90)
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After-tax monthly income
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Move any slider and the projection re-runs instantly — that is the what-if half of the Suite.
See the full range, not just the odds
Pro adds the year-by-year fan chart, pessimistic/median/optimistic balances, after-tax monthly income, and live what-if — every slider re-runs 300 paths as you drag.
80% or higher — the plan held up in most simulated histories. Worth re-checking every couple of years, not worth losing sleep over.
60–79% — workable, but thin. Raising the monthly contribution is usually the cheapest lever; adding two years of service is the second.
Below 60% — the plan depends on markets behaving. Try the sliders: contribution, years until retirement, and expected return each move the odds by very different amounts, and seeing which one moves yours is the point of the exercise.
The pessimistic (p10) figure matters more than the median. It is the outcome you should be able to survive, because one retirement in ten looks like it or worse.
How it works
Each simulated path draws its own annual return from a normal distribution centred on the rate you entered (about a 5-point standard deviation), then compounds your balance monthly and adds your contributions, raising them each year by your contribution-increase rate. Your pension is calculated the standard way — multiplier × years of service × final average salary — and the 403(b) balance is converted to income at a 4% annual withdrawal rate.
The target is 80% of your final average salary, the usual planning benchmark for replacing pre-retirement income. The success rate is simply the share of paths where your pension plus that 4% withdrawal reaches it.
Nothing you type is sent anywhere. The whole simulation runs in your browser; the only network call this page makes is an optional check of your subscription tier. Formulas are documented on the Methodology page.
What it does not model
Sequence-of-returns risk during withdrawal — the projection ends at retirement.
Social Security, spousal income, or other pensions. For two-earner households use Joint / Household Analysis.
Inflation on the income target, plan-specific COLAs, or early-retirement reduction factors.
Educational estimates only, not financial advice. Real pension formulas vary by system and vesting rules; check your plan documents before making a decision.