Coast FIRE Calculator
Coast FIRE Calculator
The amount you need invested today so that, with no more saving, it grows to your FIRE number by retirement — whether you are there yet, and if not, the monthly SIP that gets you there by a chosen age.
Coast FIRE number
Age 30, retiring at 55, $6,00,000 a year in today’s money, 4% withdrawal, $15,00,000 invested, 10% return, 4% inflation, coast by 40
The coast number and the SIP to reach it
- Y, c
- years to retirement, and years to your coast age
- n, i, g
- the return, inflation and the real return, as decimals
- target
- the coast number at your coast age, in money: F × (1 + i)Y ÷ (1 + n)Y − c
- j
- the monthly rate (1 + n)1/12 − 1, so the SIP compounds at exactly n a year; each instalment is invested at the start of the month and stays the same in money
Worked example
Age 30, retiring at 55, $6,00,000 a year in today's money, 4% withdrawal, $15,00,000 invested, 10% return, 4% inflation, coast by 40
FIRE number = 6,00,000 ÷ 0.04 = $1,50,00,000
Real return = 1.10 ÷ 1.04 − 1 = 5.77%; over 25 years money grows 4.0643 times
Coast number = 1,50,00,000 ÷ 4.0643 = $36,90,690; you have $15,00,000, a gap of $21,90,690
A SIP of $28,205 a month until 40, then nothing more, reaches $1,50,00,000 in today's money at 55
Coast number for a 1,50,00,000 FIRE number, by real return and years to retirement
| Real return | 15 years | 20 years | 25 years | 30 years |
|---|---|---|---|---|
| 4% | $83,28,968 | $68,45,804 | $56,26,752 | $46,24,780 |
| 5% | $72,15,256 | $56,53,342 | $44,29,542 | $34,70,662 |
| 6% | $62,58,976 | $46,77,071 | $34,94,979 | $26,11,652 |
| 7% | $54,36,690 | $38,76,285 | $27,63,738 | $19,70,507 |
What Coast FIRE means, and the assumptions behind it
Coast FIRE is an informal idea from the financial-independence community. If you already have enough invested that, with no further saving, it will grow to your FIRE number by the time you retire, you can “coast”: keep working to pay for today’s spending, but stop saving for retirement. The FIRE number is a year’s expenses divided by a withdrawal rate — 25 times expenses at 4% — as on the FIRE calculator.
In the example, $6,00,000 a year at 4% needs $1,50,00,000 in today’s money. At a 10% return and 4% inflation the real return is 5.77%, and over 25 years money grows 4.06 times in buying power, so $36,90,690 invested today is enough. With $15,00,000 the gap is $21,90,690; investing $28,205 a month until 40 closes it. The chart shows your investments left alone, the same with the SIP, and the FIRE number, all in today’s money. Left alone, investments either reach the number by retirement or they do not — waiting does not change that, because the target is fixed at your retirement age.
The 4% figure comes from William Bengen’s 1994 study of US stock and bond returns and the 1998 “Trinity study”: a retiree taking 4% of the portfolio in the first year, then the same amount raised by inflation, would not have run out of money over 30 years in the US history they tested. It is a finding about 30-year retirements in one country’s markets. Retiring early means money has to last longer, and inflation in India has usually been higher than in the US, so many planners use 3 to 3.5%: at 3.5% the FIRE number here would be $1,71,42,857. See the safe withdrawal rate calculator for how long a corpus lasts.
Coast FIRE depends more on the return assumption than most plans, because it rests on decades of compounding with nothing added. A lower return, a bad decade just before retirement or higher spending all move the target, and the table shows how much. Treat the coast number as a milestone to review every year or two, not a reason to stop saving for good. For the SIP arithmetic see the SIP goal calculator. This is arithmetic on the figures you enter, not financial advice.
Frequently asked questions
What is Coast FIRE?
Having enough invested that, with no more contributions, it grows to your FIRE number by your retirement age. You still work to cover today’s spending, but no longer need to save for retirement.
How is the Coast FIRE number calculated?
FIRE number ÷ (1 + real return)years to retirement. $1,50,00,000 with 25 years at a 5.77% real return is $36,90,690 today.
Why does the calculator use the real return?
Because expenses are in today’s money. Growing savings at the return after inflation keeps both sides in the same terms.
Is the 4% rule safe for early retirement?
It comes from US data over 30-year retirements. An early retirement lasts longer, and Indian inflation has usually been higher, so many planners use 3–3.5%, which raises the FIRE number and the coast number.
Related calculators
References
- Bengen WP. Determining Withdrawal Rates Using Historical Data. Journal of Financial Planning. 1994;7(4):171–180.
- Cooley PL, Hubbard CM, Walz DT. Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable. AAII Journal. 1998;20(2):16–21 (the “Trinity study”).
- Brealey RA, Myers SC, Allen F. Principles of Corporate Finance. McGraw-Hill. Present and future values, annuities, and nominal versus real rates of interest.
- Central-bank inflation targets used as default inflation by currency: Reserve Bank of India (4% CPI, flexible inflation targeting framework); U.S. Federal Reserve (2% PCE); European Central Bank (2%); Bank of England (2% CPI); Bank of Canada (2%); Reserve Bank of Australia (2–3%); Bangko Sentral ng Pilipinas (3% ± 1). Actual inflation often runs above target.