Retirement Calculator (FIRE Number)
Estimate your retirement number using the 4 % rule, and project whether your current savings + monthly contributions will get you there.
What this calculates
Retirement math is shockingly simple: figure out the annual spending you want, multiply by 25 (the 4 % rule), and you have your target portfolio. This calculator runs that math, then projects how long it'll take you to get there based on what you already have, what you save each month, and an expected return on investments.
Formula & how it works
Target portfolio = annual_spending × 25 (Trinity Study, 30-year horizon, 4 % safe withdrawal). To project growth: each year, balance × (1 + return) + annual_contribution. Solve for years until balance ≥ target. Reality: returns are not constant, and sequence-of-returns risk early in retirement matters a lot. The 4 % rule is a planning anchor, not a guarantee.
Worked example
Want $60,000/year in retirement income → target = $1.5M. Current savings $200,000, contributing $2,000/month, expecting 7 % real return. Year 1: 200K × 1.07 + 24K = 238K. Year 10: ~$725K. Year 20: ~$1.59M — crosses the line in year 20. Cut contributions to $1,000/month: takes ~27 years. Bump returns to 9 %: hit it in ~16 years.
Frequently asked questions
What's the 4 % rule?
The Trinity Study (1998) showed that retirees who withdrew 4 % of their portfolio in year 1, then increased that amount with inflation each year, almost never ran out of money in any 30-year window of historical US market data. Hence: target portfolio = 25× annual expenses.
Is 4 % too aggressive for early retirement?
For 40–50 year horizons, many planners suggest 3.5 % or even 3.25 % to be safer. That changes the multiplier to ~30× expenses. The longer the retirement, the more conservative the withdrawal needs to be.
Should I use real or nominal returns?
Real (inflation-adjusted) — typically 5–7 % for US stocks long-term. That way the target portfolio is also in today's dollars and the math is consistent. Mixing nominal returns with today's-dollar spending overshoots.
What about Social Security or a pension?
Subtract their annual value from the spending you need from your portfolio. If you spend $60K/year but expect $20K/year from Social Security at 67, your portfolio only needs to support $40K/year → $1M target instead of $1.5M.
Sources
Disclaimer: Informational only — not financial advice. Consult a fee-only fiduciary advisor for personalized retirement planning.