How Coast FIRE is calculated
Coast FIRE is one division. Work out the portfolio you need at retirement, then discount it back to today at whatever return you expect to earn between now and then. What comes out is the amount that, left alone, grows into the full number without further contributions, if those assumptions hold.
Coast number = (annual spending ÷ withdrawal rate) ÷ (1 + return)years to retirement
A worked example
You are 35, you expect to spend $50,000 a year in retirement, and you plan to stop at 65. At a 4% withdrawal rate the full target is $1,250,000. You have 30 years of growth ahead, so at a 7% real return the discount factor is 1.0730, or about 7.6. Divide and you get roughly $164,000. Reach that, and you could stop contributing today and still land on $1,250,000 at 65 — provided the assumed growth is achieved. This is a scenario, not a guaranteed outcome.
Coast FIRE number by age
The same $1,250,000 target, a 7% real return, retiring at 65. Every year you wait, the number you need today climbs — that is compounding working against you rather than for you.
| Age | Years left | Coast number |
|---|---|---|
| 25 | 40 | $83,000 |
| 30 | 35 | $117,000 |
| 35 | 30 | $164,000 |
| 40 | 25 | $230,000 |
| 45 | 20 | $323,000 |
| 50 | 15 | $453,000 |
| 55 | 10 | $635,000 |
The ratio is what matters, not the currency — read these in whatever you spend in. Change any assumption in the calculator above and the whole curve moves.
How to choose your Coast FIRE inputs
Keep savings, contributions and spending in the same currency. Count the investments intended to fund retirement, rather than money reserved for near-term bills or an emergency fund. Enter annual retirement spending in today's money, including costs the portfolio must cover such as housing, healthcare and withdrawal taxes.
The monthly contribution is converted to an annual amount and added at the end of each projected year. Social Security and pensions are entered with their start ages; investment fees and taxes are not modelled separately. The return (the S&P 500's 6.9% a year after inflation since 1928) and 4% withdrawal defaults are editable assumptions; compare lower returns and different spending before relying on the result. Even small investment fees reduce long-term growth.
The chart uses constant annual growth and shows ten years after retirement. It is not a lifetime sustainability test. Learn how the order of investment returns affects retirement withdrawals before treating a smooth projection as a promise.
Coast FIRE FAQ
What is my Coast FIRE number?
Your Coast FIRE number is the amount invested today that could grow to your retirement target without further contributions. It depends on annual retirement spending, withdrawal rate, years until retirement, and assumed real return. Current investments and monthly contributions determine when you might reach that threshold.
Does this Coast FIRE calculator account for inflation?
Yes, through the return you enter. Use an after-inflation (real) annual return and spending in today's money. Do not enter a nominal return and assume inflation will be subtracted automatically. For example, 7% nominal growth with 3% inflation is about 3.9% real growth: (1.07 / 1.03) - 1. Fees and taxes are not deducted automatically either.
Can I stop saving now, or only at my Coast FIRE age?
Those are different questions. The Coast number is the threshold for stopping contributions today. The calculator also uses your existing savings and monthly contributions to estimate the earliest age you could reach that threshold. Moving Stop paying in at compares a chosen plan with continuing to contribute until retirement. You still need income to cover living costs during the coasting years; this model assumes no portfolio withdrawals until retirement.
Is Coast FI the same as Coast FIRE?
Yes, both refer to the same milestone. Reaching it means retirement contributions could become optional under your assumptions; it does not mean work is already optional or retirement is guaranteed.
Is Coast FIRE the same as Barista FIRE?
No. Coast FIRE assumes the retirement portfolio stays invested without withdrawals while other income covers living costs. Barista FIRE usually combines part-time work with portfolio income or other resources to cover current spending. Working part time can fit either approach, but drawing from the portfolio before retirement changes the Coast FIRE calculation.
Does this Coast FIRE calculator include Social Security?
Yes. Enter your expected Social Security or pension in today's money and the age it starts. Income that starts at retirement lowers the spending your portfolio must cover. Income that starts later leaves a gap: your portfolio pays everything until then, and the calculator adds the cost of bridging those years to your target. Your Social Security statement at ssa.gov shows estimates by claiming age.
How does Coast FIRE work for couples?
Choose Two of us and enter the household's combined savings, contributions and retirement spending, plus each person's Social Security or pension. Enter the age a partner's benefit starts in your age: if your partner is three years younger and claims at 67, that is 64 for you. A second benefit usually lowers the Coast number, and a later start raises the bridge cost.
What inputs matter most for Coast FIRE?
All four target assumptions matter. Spending changes the target proportionally; a lower withdrawal rate raises it. Return and years to retirement compound together. For a $1,250,000 retirement target in 30 years, the Coast number is about $164,000 at 7% real return, $289,000 at 5%, or $515,000 at 3%. These are scenarios, not predicted returns.
Plan the next step
Use the FIRE calculator for the full number and a date, then pressure-test the withdrawal rate. Coast FIRE is the milestone between where you are and either of those.