Quick answer
Use this Coast FIRE calculator to find the savings level where compound growth alone can carry your portfolio to a retirement target — no further contributions required. The math is one line: at a 7% average return, a $1,500,000 target at 65 needs only about $197,000 banked by age 35. Hit that number and the remaining work belongs to time, not to your savings rate.
What Coast FIRE means in practice
Coast FIRE (sometimes written "CoastFIRE") is the point where your invested balance, left alone, is projected to reach your retirement number by your target age.
The formula is coast number = retirement target ÷ (1 + return)^years remaining. It is ordinary compound growth run backward. Reaching it does not mean you can stop working — it means you could stop saving for retirement and only need income that covers current spending.
For a $1,500,000 target at age 65, assuming a 7% average annual return, the coast number by age looks like this:
- Age 25 (40 years of growth): about $100,000
- Age 30 (35 years): about $140,000
- Age 35 (30 years): about $197,000
- Age 40 (25 years): about $276,000
- Age 45 (20 years): about $388,000
- Age 50 (15 years): about $544,000
The doubling pattern is the whole story: every decade you wait roughly doubles the balance required, because you are giving up a doubling of growth.
How to use this calculator
1. Pick one target method
Set the retirement target either directly or as annual spending ÷ withdrawal rate. At a 4% withdrawal rate, $60,000 of spending implies a $1,500,000 target; $80,000 implies $2,000,000.
2. Enter age timeline and current savings
Current age, target retirement age, and today's invested balance. The gap between your balance and the coast number for your age is the actionable output.
3. Set return and inflation assumptions
Use a real (after-inflation) return with a today's-dollars target, or a nominal return with an inflated target — never mixed. At a real 5% instead of a nominal 7%, the age-35 coast number for the $1,500,000 example rises from about $197,000 to about $347,000. The assumption choice is worth more than most contribution decisions.
4. Read status and savings gap outputs
If you are short of the coast number, the tool shows the gap. Closing a $50,000 gap at age 30 is worth roughly $500,000 of not-needed savings later — that is the trade you are pricing.
High-impact assumptions
Years remaining and the return assumption dominate this formula; the target itself only scales it.
Time to retirement
Each year of delay raises the coast bar by your assumed return. Moving the same $1,500,000 target from 65 to 60 raises the age-35 coast number from about $197,000 to about $276,000 — early retirement makes coasting meaningfully harder, not easier.
Return assumptions
The formula divides by (1 + return)^years, so the assumption compounds against you. Between 5% and 7% at 30 years out, the required balance differs by about 75%. Run both; if you only coast under the optimistic case, you are not coasting yet.
Spending target and withdrawal framework
Because the target is spending ÷ withdrawal rate, a $6,000-per-year spending trim lowers a 4% target by $150,000 — and lowers today's coast requirement by that amount discounted, about $20,000 at age 35. Our safe withdrawal rate guide covers how to pick the rate honestly.
Contribution behavior after reaching coast status
Coasting is permission, not instruction. Continuing even $250 per month past the coast point at 7% adds roughly $300,000 by a 65-year-old finish line from age 35 — margin that covers weak markets, higher spending, or an earlier exit.
Coast FIRE, Barista FIRE, and Lean FIRE
These labels describe different uses of the same arithmetic:
- *Coast FIRE*: retirement savings finished; current income only needs to cover current spending.
- *Barista FIRE*: a variant where part-time income covers part of spending while the portfolio finishes compounding — often paired with employer healthcare.
- *Lean FIRE*: full early retirement on a deliberately low spending target, such as $40,000 per year (a $1,000,000 target at 4%).
Coast is the least demanding of the three because it never asks the portfolio to support withdrawals early. That is also its risk: the plan still depends on decades of employment income for spending.
Common mistakes to avoid
1. Treating coast status as permanent
Status depends on assumptions holding. A multi-year weak market or a higher spending target can move you back below the line. Recheck annually.
2. Confusing Coast FIRE with full retirement readiness
Coast means the future is funded, not the present. You still need income until the target age.
3. Ignoring healthcare and lifestyle drift
A target set at $60,000 spending fails quietly if real spending drifts to $75,000 — that drift raises the target by $375,000 at a 4% rate.
4. Over-relying on one return estimate
Coast status at 7% and non-status at 5% is not status; it is a bet. Require the conservative case to at least come close.
5. Forgetting account accessibility
A coast plan finishing at 65 inside retirement accounts is straightforward. One finishing at 50 needs taxable or Roth-basis money to bridge early years — the FIRE calculator with multiple accounts models that split.
Interpreting the formula without overconfidence
The clean arithmetic hides sequence risk: the formula assumes a smooth average return, but a decade of poor returns immediately after you stop contributing leaves less capital to compound later, even if the long-run average recovers. Treat the coast number as a floor to exceed, not a finish line to touch — a 10% to 20% buffer above it absorbs most historical bad sequences at long horizons.
A practical decision checklist
- Compute the coast number at your realistic and conservative return assumptions.
- Compare your invested balance to both.
- If you clear the conservative number, decide deliberately what the freed-up savings should do next: mortgage payoff, taxable bridge fund, or spending.
- If you clear only the optimistic number, keep contributing and recheck yearly.
- Rerun after any change to the target age, spending plan, or allocation.
Where this calculator fits in your workflow
Start with the FIRE calculator to establish the target and timeline, use this page to test whether compounding alone can finish the job, then use the Retirement Goal Calculator to backsolve contributions for any remaining gap. When the plan involves multiple account types or an early bridge period, continue with the FIRE calculator with multiple accounts.
Frequently asked questions
If I am Coast FIRE, should I stop saving?
You have the option, not an obligation. Most people redirect rather than stop: taxable bridge savings, mortgage principal, or simply margin. Every $100,000 of extra cushion at 7% is worth about $200,000 a decade later.
Does this work for early retirement targets?
Yes, but the bar rises fast — see the 65-to-60 example above. Early targets also add a healthcare and account-access bridge that this simple formula does not price.
Should I include Social Security in this model?
Treat it as a buffer rather than a reduction of the target for long horizons. If you do reduce the target, run the no-benefit case too.
Why does inflation input matter here?
Because the formula's exponent runs across decades. Mixing a nominal return with a today's-dollars target understates the true coast number by the full compounded inflation gap — at 3% over 30 years, a factor of roughly 2.4.
What if market returns are weaker for several years?
Your coast number rises when recomputed at the lower realized balance. That is the system working: recheck annually, and hold the buffer described above so ordinary bad decades do not break the plan.
Educational use note
This content is educational and scenario-based. It is not financial, legal, or tax advice. Use conservative assumptions, compare multiple scenarios, and consult qualified professionals before making irreversible decisions.