A coast fire calculator finds the amount you need invested today so that growth alone can reach your full retirement number by a chosen date. Formula: Full number = annual spending ÷ withdrawal rate; Coast FIRE number = full number ÷ (1 + return)^years. With $60,000 of yearly spending, a 4% withdrawal rate, a 5% return and 20 years to go, the full number is $1,500,000 and the coast figure today is $565,334.22.
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How to use the coast fire calculator
- Enter the yearly spending you expect in later retirement, in today’s dollars.
- Choose a withdrawal rate. Many planners test 3.5% to 4%.
- Enter the yearly return you expect until you start withdrawals. Using a return after inflation keeps everything in today’s dollars.
- Enter the years until withdrawals start and the amount you already have invested.
The coast fire calculator shows the full retirement portfolio, the Coast FIRE number today and how far you still are from it.
What formula does the coast fire calculator use?
- Full retirement number = annual spending ÷ withdrawal rate. $60,000 ÷ 4% = $1,500,000.
- Coast FIRE number = full number ÷ (1 + return) raised to the number of years.
- Gap = Coast FIRE number − savings today, never below zero.
The coast fire calculator assumes a steady return each year and no new deposits or withdrawals before the start date. It is the present value of the full number, nothing more.
Coast fire calculator worked example
Starting from $60,000 of spending, a 4% withdrawal rate, a 5% return, 20 years and $150,000 saved, here is what changes when you move one input:
| Change | Full number | Coast FIRE number | Still to save |
|---|---|---|---|
| Defaults | $1,500,000 | $565,334.22 | $415,334.22 |
| 30 years instead of 20 | $1,500,000 | $347,066.17 | $197,066.17 |
| 7% return instead of 5% | $1,500,000 | $387,628.50 | $237,628.50 |
| $40,000 spending | $1,000,000 | $376,889.48 | $226,889.48 |
| 3.5% withdrawal rate | $1,714,285.71 | $646,096.26 | $496,096.26 |
Time matters most. Ten more years of growth cuts the coast figure by about 39%, while a lower withdrawal rate raises it sharply.
What “coasting” means in practice
Coast FIRE is a milestone, not full retirement. Once your investments reach the coast figure, you still work to pay today’s bills, but you could stop adding to retirement accounts and, if the assumptions hold, still reach the full number. Some people use that point to take a lower-paid job, cut hours or go part time.
The risk is in the assumptions. A coast fire calculator cannot know future returns, and a bad decade early on can leave you short. Rerun it each year with your real balance, and keep contributing at least enough to capture any employer match.
Choosing a return and withdrawal rate
If you enter a return that already subtracts inflation, the full number stays in today’s dollars, which is easier to compare with your budget. If you enter a return before inflation, raise the spending figure to the future amount you expect. The SEC’s Investor.gov compound interest calculator is a good way to check how sensitive a balance is to the rate you pick.
A 4% withdrawal rate is a common starting point for long retirements, not a guarantee. People retiring early, with 40 or more years to fund, often test 3.25% to 3.5% instead.
Example: a couple at 35
A couple at 35 has $210,000 in index funds and wants to spend $70,000 a year from age 60. At a 4% withdrawal rate they need $1,750,000. Over 25 years at a 5% real return the coast fire calculator gives about $516,780, so they are about $306,780 short. At a 6% return the figure drops to about $408,000. They decide to keep saving for five more years and recheck.
Five years later, at 40, their balance has grown to $330,000 with steady contributions. With 20 years left at 5%, the coast fire calculator now asks for about $659,600, so the gap is about $329,600, a little larger than before. Five fewer years of growth raised the coast figure faster than their savings grew. That is the usual trap: coasting gets harder the longer you wait, so the earlier you reach the figure, the more the market does for you. Checking once a year, after updating the balance, is enough.
Estimates for education only, not tax, legal or financial advice. Check current rules with the tax authority or a qualified adviser.
Related converters and calculators
Related calculators:
- Retirement calculator: savings target
- Compound interest calculator: growth
- Investment calculator: future value
Sources
Investor.gov: Compound interest calculator; Investor.gov: Compound interest.
Questions about this calculator
What is a Coast FIRE number?
It is the amount invested today that can grow, without new contributions, into the portfolio your retirement spending needs.
How is the full retirement number figured?
Divide your yearly retirement spending by the withdrawal rate. $60,000 at 4% gives $1,500,000.
Should I use a real or nominal return?
A real return, after inflation, keeps the answer in today's dollars and makes it easier to compare with your budget.
Does reaching Coast FIRE mean I can quit work?
No. It means you can stop saving for retirement, but you still need income for current costs.
What withdrawal rate should I use?
Many people test 3.5% to 4%. Lower rates are more conservative for long retirements.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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