retirement · 2026-05-01
Compute your Financial Independence / Retire Early target — Lean FIRE, regular FIRE, Fat FIRE — based on annual spending and safe withdrawal rate.
| Target annual spending | $50,000 |
| Safe withdrawal rate % | 4% |
| Current invested assets | $350,000 |
| Annual savings rate | $50,000 |
| Expected real return % | 5% |
| FIRE number | $1,250,000 |
| Lean FIRE (spend × 25 ÷ 1.4) | $892,857 |
| Fat FIRE (spend × 25 × 1.5) | $1,875,000 |
The FIRE math is simple: 25× annual spending = the portfolio that supports it indefinitely at 4% withdrawal. The hard parts are the assumptions: how stable is your spending, what's your real return, what's your post-FIRE healthcare plan?
Bengen's 1994 study tested 4% across all 30-year retirement periods 1926-1990. It survived. But:
100% US large-cap stocks 1926-2023: ~7% real (after inflation). 60/40 stocks/bonds: 5-6% real. International-diversified portfolios: 4-5% real. Going forward: most major firms (Vanguard, BlackRock CMA) are projecting 3-5% real for 60/40 over the next decade due to high valuations and low yields. Use 5% real as a defensible base case; 4% real if you're conservative.
Determines time-to-FIRE more than anything: 50% savings rate → ~17 years; 65% → ~10 years; 25% → ~32 years. Math derivation: years_to_FIRE ≈ ln(1 / (1 − savings_rate)) / ln(1 + return). Get savings rate above 50% and FIRE compresses dramatically.
Depends on how much you'd hate cutting back at 65 if Lean FIRE math turns out wrong. Hedge: target Regular FIRE numerically, but plan to do part-time work for 5-10 years post-FIRE that covers ~30% of spending. This drops the actual portfolio drawdown and adds enormous resilience to sequence-of-returns risk.