Retirement Calculator: Will Your Money Outlive You?
Retirement planning intimidates people because it combines three hard things: decades-long projections, market uncertainty, and honest self-assessment about spending. This free retirement calculator reduces the problem to its essential question — given what you're saving and how it grows, how big will your nest egg be, and will it support the retirement you want? Adjust any input and watch the answer recalculate instantly.
How the Calculator Projects Your Nest Egg
Two forces build your retirement fund, and both compound:
- Your current savings grow untouched: FV = P × (1 + r)^n
- Your monthly contributions form an annuity: FV = M × ((1+r)^n − 1) / r
The calculator simulates this month by month (r = annual return ÷ 12) and plots the full growth curve from your current age to retirement age. A realistic projection uses real returns — the return after inflation. Since 1926, a diversified U.S. stock portfolio has averaged roughly 10% nominal, or about 7% real. That's why 7% is the default here: it means your results are in today's dollars, automatically adjusted for rising prices.
The 4% Rule and Your FIRE Number
Once you have a nest egg, how much can you safely spend? The famous 4% rule comes from the Trinity Study (1998), which tested historical withdrawal rates across 30-year retirements. Conclusion: withdrawing 4% of the portfolio in year one, then adjusting that dollar amount for inflation annually, survived nearly every historical period — including those beginning just before the 1929 crash.
The rule implies a simple target. Since 4% × 25 = 100%:
Safe nest egg = 25 × annual spending
Want to live on $40,000/year from your portfolio? You need $1,000,000. That figure — 25× expenses — is the "FIRE number" the calculator shows next to your projection. Comparing the two numbers instantly answers whether you're on track, ahead, or facing a gap.
Worked Example
A 30-year-old with $50,000 saved, contributing $500/month, expecting 7% real returns, retiring at 65, and planning to spend $40,000/year:
- Years to retirement: 35
- The $50,000 compounds to roughly $570,000
- Monthly contributions add about $900,000 more
- Projected nest egg: ≈ $1.48 million
- Safe annual withdrawal at 4%: ≈ $59,000 — comfortably above the $40,000 target
- FIRE number: 25 × $40,000 = $1,000,000 → on track with a cushion
Now the part that surprises people: move the starting age from 30 to 40. The projection collapses by roughly half a million dollars. Ten years of compounding — not the contributions themselves, which total only $60,000 — accounts for most of that gap. Time in the market is the single most powerful variable in retirement math.
Choosing Your Inputs Wisely
- Return rate — 7% is a reasonable long-run diversified estimate; use 5% for a conservative mix with more bonds; 4% if retiring within a few years
- Retirement age — matters doubly: it lengthens compounding and shortens the withdrawal period
- Spending — most retirees spend roughly 70–80% of their working-life expenses, but healthcare often rises; be honest rather than optimistic
- Social Security/pension — this calculator models personal savings only. If you'll receive $1,800/month from Social Security, subtract $21,600 from your target spending and aim at the remainder
Beyond the Math: Sequence Risk and Flexibility
No projection is a promise. The greatest danger is sequence-of-returns risk: retiring into a bad market early in withdrawal can permanently damage a portfolio even if long-run averages hold. Mitigations: hold 1–2 years of expenses in cash when approaching retirement, keep a flexible spending rule (skip inflation adjustments after down years), and consider delaying Social Security to age 70 — each delay year boosts benefits roughly 8%.
Frequently Asked Questions
The FAQ under the calculator covers the 4% rule, choosing return assumptions, accounting for Social Security, and closing a monthly savings gap.
Disclaimer
Projections are mathematical estimates based on your assumptions, not predictions or guarantees. Markets fluctuate; actual results will differ. This tool is educational and is not investment, tax, or financial advice. Consult a fiduciary financial advisor for personal guidance.