Coast FIRE

How Coast FIRE Is Calculated

Coast FIRE is the balance you’d need today that, left completely untouched with no further contributions, would grow through compounding alone to a full FIRE number by your retirement age. Enter your current age, target retirement age, current retirement savings, expected annual expenses at retirement, and expected annual return, and this calculator finds your Coast FIRE number and tells you whether you’ve already reached it.

This is distinct from the FIRE Calculator calculator, which assumes you keep contributing until you retire — Coast FIRE specifically asks whether you could stop contributing right now and still be on track.

Key Factors to Consider

• “No further contributions” is the planning assumption behind the math, not necessarily good advice to actually follow. Most people who reach Coast FIRE still keep contributing enough to capture a full employer 401(k) match, since turning down free matching money rarely makes sense even after hitting this milestone — reaching Coast FIRE is more often treated as a flexibility marker (the freedom to work less, change careers, or take a lower-paying but more fulfilling job) than a literal instruction to stop saving.
• Retiring well before Medicare eligibility (age 65 in the U.S.) means budgeting for health insurance separately. The standard 25x-expenses FIRE number doesn’t specifically account for the often-substantial cost of private health coverage during an early-retirement gap — worth adding to the annual expenses figure if coasting toward a retirement age well under 65.
• Whether your return rate and expenses are in “real” or “nominal” terms matters. If your expected annual return assumption already accounts for inflation (a “real” return, commonly cited around 5-7% after inflation for a diversified stock portfolio), your annual expenses should be in today’s dollars. Mixing a nominal (non-inflation-adjusted) return with today’s- dollar expenses, or vice versa, will meaningfully skew the result.
• Market performance right around the actual retirement date matters more than the long-run average return assumption. A downturn in the years just before or after actually retiring can affect a portfolio’s ability to sustain withdrawals (“sequence-of-returns risk”), even when the average return used in this calculation holds true over the full multi-decade period.

The Formula

$$\vB{\text{FIRE Number}} = \vA{\text{Annual Expenses}} \times 25$$ $$\vD{\text{Coast FIRE Number}} = \frac{\vB{\text{FIRE Number}}}{(1+r)^{n}}$$

where $n$ is the number of years until retirement.

Worked Example

At age 30, planning to retire at 65 (35 years away), expecting to spend $40,000 a year in retirement, at a 7% annual return:

1. FIRE Number: $\vA{40{,}000} \times 25 = \vB{1{,}000{,}000}$.
2. Coast FIRE Number: $\frac{\vB{1{,}000{,}000}}{(1.07)^{35}} \approx \vD{93{,}663}$.

With $150,000 already saved — well above the $93,663 Coast FIRE number — this visitor has already reached Coast FIRE, and that balance alone would grow to about $1,601,487 by age 65 with no further contributions.

Useful to Know

Reaching Coast FIRE doesn’t have to mean an all-or-nothing switch away from saving — many people treat it as a checkpoint that unlocks other tradeoffs, like taking a lower-paying but more enjoyable job, cutting back to part-time work, or simply feeling less anxious about short-term market swings since the retirement math already works out. Because the Coast FIRE number shrinks the closer you get to your target retirement age (there are fewer years left for compounding to do the work), it’s worth recalculating every year or two as your age, savings, and expense expectations change, rather than treating one calculation as a permanent answer.