Quick answer
Coast FIRE is the point where your invested savings, left untouched, will grow into a full retirement pot by retirement age without another contribution. If you need $50,000 a year in retirement and expect a 7% return, the full pot is $1,250,000 and the coast number at 30 is about $117,000 — invest that by 30 and compounding does the rest.
How the Coast FIRE Calculator works, step by step
Enter your expected annual spending in retirement, your current age, retirement age and expected return. The calculator first sizes the full retirement pot using the 25× spending rule (spending divided by a 4% withdrawal rate), then discounts it back to today at your return to find the coast number — the amount that, invested now, reaches the full pot on its own.
Add what you have already invested and a monthly contribution to find your coast date: the number of months of contributing until your balance crosses the coast number. On the default figures — $50,000 invested, $500 a month — the gap to the $117,079 coast number is $67,079, closed in about 70 months, or just under six years. Your $50,000 alone, left untouched, would reach only about $533,829 by 65.
Respect the assumptions. The coast number is acutely sensitive to the return: at 5% instead of 7%, the 30-year-old's target rises from about $117,000 to about $227,000; at 6% it is about $163,000. A coast plan built on an optimistic return is a plan to return to full saving later, so test the 5% case before treating the coast number as a promise.
Use a real (after-inflation) return to keep the maths in today's money. A 7% nominal return with 2% to 3% inflation is roughly a 4% to 5% real return — and at 5% the coast number nearly doubles. The calculator takes the return you enter at face value, so enter the after-inflation figure if your spending target is stated in today's dollars, as it is here.
Social Security shrinks the target. The average retired-worker benefit was about $2,071 a month in 2026 after the 2.8% cost-of-living adjustment — roughly $24,850 a year. If benefits cover $25,000 of your $50,000 spending, the portfolio only needs to supply $25,000 and the full pot falls from $1,250,000 to $625,000. Conservative planners discount the benefit rather than ignoring it entirely.
The formula
Full retirement pot = Annual retirement spending × 25. Coast number = Full pot ÷ (1 + return)^(years until retirement). Months to coast are simulated: balance grows monthly at return ÷ 12 plus the monthly contribution until it reaches the coast number.
Worked example — try it on the calculator above
Worked example: coast number at 30 for retirement at 65
Planned retirement spending: $50,000 a year, so the full pot target is $50,000 × 25 = $1,250,000. Discount at 7% over 35 years: $1,250,000 ÷ 1.07^35 = $117,079. Invest roughly $117,000 by age 30 and, if 7% materialises, the pot reaches $1,250,000 at 65 with no further contributions. Already holding $50,000 at 30 leaves a gap of about $67,000 — at $500 a month, roughly 70 months of contributing before you can coast. Already past the number? The calculator reports 'Already Coasting' and the gap shows as zero.
Frequently Asked Questions
Where does the 25× spending figure come from?
It is the inverse of the 4% withdrawal guideline: a pot of 25 times annual spending can pay out 4% in the first year and adjust for inflation, and historically that has usually lasted 30 years. It is a planning heuristic from US market data, not a guarantee — lower expected returns argue for 28× to 33× (a 3% to 3.5% withdrawal rate).
Does Coast FIRE mean I can stop working?
No — it means you can stop saving for retirement. You still need income to cover living costs between now and retirement age. What changes is the type of work you can accept: a lower-paid, less stressful or part-time job that covers expenses becomes viable because retirement is already funded in the background.
Should Social Security change my coast number?
It reduces the pot you need. If Social Security will cover $25,000 of your $50,000 spending, the portfolio only needs to supply $25,000, and the target falls from $1,250,000 to $625,000. Conservative planners discount the benefit (for example by 25%) rather than ignoring it entirely, given the programme's projected funding shortfall.
What return should I use for the coast calculation?
A real (after-inflation) return keeps the maths in today's money: roughly 4% to 5% for a stock-heavy portfolio if you expect 7% nominal returns and 2% to 3% inflation. Using the nominal return against today's spending target overstates your progress — the most common Coast FIRE error.
Estimates, not advice. This calculator provides educational estimates based on the inputs you enter and the assumptions shown on this page. It is not financial, tax or investment advice, and it cannot see your full situation. Verify important figures against official sources, and consider a qualified professional for decisions about your own money. See our Disclaimer and Methodology.