What this calculator does
Most retirement calculators grow your savings at one average return and draw a single smooth line. Real markets don't move in a straight line, and the order of good and bad years matters enormously once you're withdrawing. This tool plays your plan through 1,000 simulated return paths — independent random annual draws calibrated to your allocation, not replays of actual history — and counts how often you make it. The result is a simulated success rate under these assumptions, not a forecast or a promise.
The assumptions
All figures are in today's (inflation-adjusted) dollars:
- Returns follow your allocation. Your stocks % sets the expected real return and volatility — the same blend table the full app uses (60/40 ≈ 5.2% real, 12.7% volatility).
- Contributions are added every year through your retirement age; spending begins the year after and stays constant in real terms (unless you turn on the age-decline pattern, which glides real spending down gradually from 70 to 80% by 85).
- Social Security: enter your benefit at full retirement age; we adjust it for your claim age with the same SSA factors as the full app. If you claim before your FRA while still working, no benefit is credited for those working years — SSA's earnings test withholds it.
- Success means you never run out of money before your plan-to age. At 1,000 paths, treat the percentage as ±2–3 points of sampling wiggle, not decimal-precise.
- Not modeled: taxes (results are pre-tax dollars), healthcare costs, and investment fees. Fees matter — a 0.5%/yr fee is roughly a 0.5% lower real return; subtract yours mentally or use a lower stocks % as a crude proxy. The full app models taxes, account types, RMDs, ACA and Medicare.
What a "good" number looks like
- 90%+ — a robust plan. Most planners treat this as the target.
- 75–90% — solid, but worth stress-testing. Small changes to spending or retirement age move the needle.
- Below 75% — consider saving more, spending less, working a little longer, or a more flexible withdrawal approach.
Not financial advice. This is an educational estimate based on the assumptions above, which you can't fully change in this quick version. It is not investment, tax, or legal advice. For decisions specific to your situation, consult a qualified professional. The exact math is documented on the methodology page.