Coast Fire Calculator
Coast fire calculator works out FIRE number and Annual spending used from Retirement spending, in today’s money, Safe withdrawal rate and Your age now. The default figures on this page give coast FIRE number today of 395,331.94; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- FIRE number = annual spending / safe withdrawal rate = 60000 / 0.04 = 1500000 (that is 25 times spending).
- Real return = (1 + 0.07) / (1 + 0.03) - 1 = 0.03883495, so the FIRE number stays in today's money.
- Growth factor over 35 years = (1 + 0.03883495)^35 = 3.7942798.
- Coast FIRE number = FIRE number / that factor = 1500000 / 3.7942798 = 395331.94.
- Your 100000 left completely alone becomes 379427.98 by age 65.
Coast target by agetable
| age | coastTarget | projectedIfStoppedNow | projectedWithContributions |
|---|---|---|---|
| 30 | 395,331.94 | 100,000 | 100,000 |
| 35 | 478,293.71 | 120,985.34 | 185,830.06 |
| 40 | 578,665.29 | 146,374.54 | 289,671.85 |
| 45 | 700,100.2 | 177,091.74 | 415,305.2 |
| 50 | 847,018.63 | 214,255.05 | 567,303.14 |
| 55 | 1,024,768.41 | 259,217.21 | 751,198.37 |
| 60 | 1,239,819.59 | 313,614.83 | 973,684.65 |
| 65 | 1,500,000 | 379,427.98 | 1,242,860.44 |
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
Keep this result
Save it, change one figure, then compare the two
The calculation stays free. Save this scenario, adjust one assumption, save that too, and put them side by side to see exactly what the change costs you. A free account keeps 5 scenarios and 2 comparisons; Personal makes both unlimited and adds exports and private links. Nothing is saved unless you press Save.
What the coast fire calculator calculates
Turns a target retirement spend into the portfolio that supports it at a chosen safe withdrawal rate, then works out the Coast FIRE number - the amount that only has to be invested today for compounding alone to reach it by your retirement age.
How to use this coast fire calculator
Enter Retirement spending, in today’s money, Safe withdrawal rate, Your age now and Age you want to retire. FIRE number updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind FIRE number, Annual spending used and Real return after inflation.
The method follows Bengen WP, Determining Withdrawal Rates Using Historical Data, Journal of Financial Planning, October 1994 - the origin of the 4% initial withdrawal rate, Cooley PL, Hubbard CM, Walz DT, Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable, AAII Journal, February 1998 - the Trinity study portfolio success rates and Irving Fisher, The Theory of Interest (1930) - the exact relation between nominal rate, inflation and real rate used here.
What you can compare
Change one input at a time to see how it affects FIRE number, Annual spending used and Real return after inflation. The inputs you can vary are Retirement spending, in today’s money, Safe withdrawal rate, Your age now, Age you want to retire, Invested assets you already have and Amount you invest each year from here.
Understanding FIRE number, Annual spending used and Real return after inflation
A safe withdrawal rate is a historical observation, not a guarantee. This projection uses one constant real return and one constant spend; real sequences of returns, taxes, healthcare and a changing life do not behave that way.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How to calculate your coast FIRE?
Turns a target retirement spend into the portfolio that supports it at a chosen safe withdrawal rate, then works out the Coast FIRE number - the amount that only has to be invested today for compounding alone to reach. Open “How this is worked out” beside the result to see each step for your own figures.
What is the best Coast FIRE calculator?
Turns a target retirement spend into the portfolio that supports it at a chosen safe withdrawal rate, then works out the Coast FIRE number - the amount that only has to be invested today for compounding alone to reach. On this page it is computed from Retirement spending, in today’s money, Safe withdrawal rate and Your age now and shown as FIRE number, Annual spending used and Real return after inflation.
How much to coast FIRE at 30?
On the figures this page opens with — retirement spending, in today’s money 60,000 USD and safe withdrawal rate 4% — the coast FIRE number today is 395,331.94. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
Is 500k enough for coast FIRE?
Turns a target retirement spend into the portfolio that supports it at a chosen safe withdrawal rate, then works out the Coast FIRE number - the amount that only has to be invested today for compounding alone to reach. On the figures this page opens with — retirement spending, in today’s money 60,000 USD and safe withdrawal rate 4% — the coast FIRE number today is 395,331.94. Put your own figures in their place and the working updates beside the result.
What information do I need for the coast fire calculator?
You need Retirement spending, in today’s money, Safe withdrawal rate, Your age now, Age you want to retire, Invested assets you already have, Amount you invest each year from here, Expected nominal annual return and Expected inflation. The page opens with default figures that give coast FIRE number today of 395,331.94, so you can see the scale before entering your own.
What does this coast fire calculator show?
It shows FIRE number, Annual spending used, Real return after inflation, Years until retirement, Coast FIRE number today, Still needed to reach Coast FIRE, Amount past Coast FIRE and Coast FIRE reached?, with the working and any warnings for your entries.