Full financial independence is a long project. Coast FIRE is a much nearer milestone with an immediate practical consequence: once you reach it, you only need to cover current living costs, because the retirement portion of the plan is already funded.
This guide sets out the formula, gives the required balance at each age for two common targets, and explains what the milestone does and does not buy you.
How Coast FIRE Is Calculated
Coast FIRE inverts the usual compounding question. Instead of asking what a balance becomes, it asks what balance today becomes the target by a chosen date with no further deposits:
Coast number = target ÷ (1 + r)t
Where r is the expected real return and t the years until retirement. Using a real return — nominal minus inflation — lets you set the target in today's money, which is the only way the figure stays meaningful over 30 years.
Example: a 32-year-old targeting $1.5 million in today's money at 65 has 33 years and assumes 5% real. (1.05)33 = 5.003, so the coast number is $1,500,000 ÷ 5.003 = $299,800. Once the portfolio passes roughly $300,000, no further contributions are required for the 65 target.
Required Balance by Age
Both columns assume a 5% real return and retirement at 65, with the target expressed in today's purchasing power.
| Current age | Years to 65 | Coast to $1,000,000 | Coast to $1,500,000 |
|---|---|---|---|
| 25 | 40 | $142,000 | $213,000 |
| 30 | 35 | $149,000 | $224,000 |
| 35 | 30 | $231,000 | $347,000 |
| 40 | 25 | $243,000 | $365,000 |
| 45 | 20 | $377,000 | $565,000 |
| 50 | 15 | $397,000 | $595,000 |
| 60 | 5 | $619,000 | $928,000 |
The figures rise steeply with age because there is less time for growth to do the work. A 25-year-old needs about 14% of the $1 million target; a 60-year-old needs 62% of it. That gradient is the clearest argument for front-loading contributions in your twenties and early thirties.
Model your own target, age and return assumption in the FIRE retirement calculator to find where your current balance sits against the coast line.
What Reaching Coast FIRE Actually Changes
Crossing the coast threshold does not mean stopping work. It means the retirement savings requirement disappears from the budget, which changes the kind of work you can accept:
- A lower-paid job becomes viable. If living costs are $45,000 and no retirement contributions are needed, roles paying far less than your current salary become genuinely affordable.
- Part-time or seasonal work works. Covering current expenses is a much lower bar than covering expenses plus 20% of income invested.
- Career risk becomes affordable. Starting a business, retraining or taking a sabbatical no longer sets retirement back, only delays extra accumulation.
The assumptions to watch
The whole calculation rests on the real return assumption, and it is compounded over decades, so small errors matter. Using 7% real instead of 5% cuts the 30-year coast number by nearly 40% — a pleasant number that history does not reliably support. Using 4-5% real is the conservative choice.
Second, coasting only works if the portfolio is genuinely left alone. Withdrawing from it during a career break, or shifting heavily to cash for two decades, breaks the projection. Third, recheck the number every few years: if your expected retirement spending rises, the target rises and you may no longer be coasting.
Three Things That Break a Coast FIRE Plan
Coast FIRE looks clean on a spreadsheet because it assumes a single return rate applied smoothly for decades. Reality intrudes in three predictable ways, and each is manageable if you plan for it.
The return assumption is optimistic. Coasting on a 7% real return leaves no margin if the next twenty years deliver 5%. A portfolio coasting from $200,000 at age 35 reaches roughly $1.5m by 65 at 7%, but only about $865,000 at 5%. Running your number at a rate one to two points below your assumption shows how much cushion you actually have.
Spending grows with income. The coast number is derived from a target retirement spend. If that target drifts upward over the coasting decades — larger home, private schooling, higher baseline lifestyle — the balance you stopped contributing to is quietly no longer sufficient. Recalculate every two or three years against current spending, not the figure you used when you started.
Contributions stop permanently. The theory allows you to stop contributing; the safer practice is to reduce rather than stop. Continuing even a small automatic contribution keeps the account habit alive and absorbs a portion of any shortfall without requiring a difficult restart later.
Treat Coast FIRE as permission to lower the pressure, not as a finished plan. The milestone is real and worth celebrating, but the review schedule is what keeps it true.