Coast FIRE — real-return band + historical success rate
Are your current investments already enough to grow into your FI number by retirement, with zero further contributions? Most calculators answer with one checkmark at a single 7% guess. This quotes the coast number across a 3 / 5 / 7% real-return band, then replays every start year since 1928 on S&P 500 total return, CPI-deflated, to show the share of history in which coasting actually worked.
Real terminal value at retirement
history p5 · median · p95 vs assumed bandCoral = 5th-percentile historical outcome, green = median, lime = 95th-percentile — your assets replayed through every actual window, in today's dollars. The band spans the deterministic 3%→7%-real projection, so you can see where the constant-rate assumption sits inside the historical spread.
Realized real CAGR per start year
path dispersion, not sequence riskBars right of the “needed” line are start years where coasting reached your FI number; bars left fell short. With a lump sum and no cash flows, terminal value is a pure product of returns — order cannot change it — so this spread is realized-CAGR path dispersion across start years, not “sequence risk” (sequence risk needs contributions or withdrawals to exist).
Show the math ›
Assumptions & sources ›
| Assumption | Value | Source · asOf |
|---|---|---|
| Equity return (backtest) | S&P 500 total return | Damodaran (NYU Stern), annual · asOf 2026-01 · dividends reinvested |
| Inflation (real dollars) | CPI-U, Dec/Dec | BLS · asOf 2026-01 · every window deflated to today's dollars |
| Coverage | 1928–2025 | every start year with a full coast-horizon window |
| Coast band | 3 / 5 / 7% real | illustrative assumption band, quoted alongside the historical replay — not a forecast |
| Withdrawal rate | 3.0–5.0% (default 4.0%) | user assumption; the 4% figure traces to Bengen (1994) / Trinity (1998) 30-year studies |
| Taxable drag | 1.9% yield × 15% div tax /yr + 15% LTCG at horizon | illustrative qualified-dividend and long-term rates; state tax and bracket detail not modeled (v1) |
| Social Security | flat annual offset, today's $ | simple spending offset; claiming age, COLA timing and benefit taxation not modeled (v1) |
| Withdrawal-stage tax | not modeled | tax-advantaged mode ignores tax due on eventual withdrawals — the FI number is treated as pre-withdrawal-tax |
Coasting is a lump-sum projection: 100% US large-cap equity, no rebalancing, no further contributions. All outputs are estimates in today's dollars and always quoted as a range (band or p5/median/p95) — a single-rate checkmark is a point estimate, and the history above shows how wide the actual spread has been.
Common questions
What is a Coast FIRE number? ›
A Coast FIRE number is the amount invested today that could grow into your full FI number by retirement with zero further contributions. This page does not quote it as one figure. It shows the coast estimate across a 3, 5, and 7 percent real-return band, then replays every start year since 1928 on S&P 500 total return, deflated to today's dollars, to show the share of history in which coasting actually reached the target.
How is the Coast FIRE number calculated? ›
The FI number is spending minus any Social Security offset, divided by your chosen withdrawal rate, defaulting to 4 percent, which traces to the Bengen 1994 and Trinity 1998 studies. The coast number is the smaller sum that compounds into that FI number over the horizon of retirement age minus current age, at an assumed real return. A fee in basis points and a taxable-account drag can be subtracted from the growth each year.
Does Coast FIRE have sequence-of-returns risk? ›
No. Coasting is a lump sum left alone with no contributions or withdrawals, so the terminal value is a pure product of the returns, and their order cannot change it. The spread you see across start years is realized-CAGR path dispersion, meaning some historical windows compounded faster than others. Sequence-of-returns risk needs cash flows to exist, so it belongs to the withdrawal phase, not to the coast itself.
What real return does the Coast FIRE calculator use? ›
Instead of a single guess, the calculator quotes the coast number at 3, 5, and 7 percent real return, an illustrative band rather than a forecast. Alongside it, the tool replays S&P 500 total return for every start year from 1928 that has a complete window of your length (returns data through 2025), CPI-deflated, so you can see where the constant-rate assumption sits inside the actual historical spread. Results are stated in today's dollars and always as a range.
Related
- Guide: Coast vs Barista FIRE
What actually separates the two milestones.
- Savings rate → FI
How your savings rate maps to years until FI.
- Real vs nominal returns
Why the coast band is quoted in real terms.
- Methodology
How the rolling-window engine and data layers are built.