Finance Calculator
Coast FIRE Calculator
Find out how much you would need invested today for growth alone to carry you to retirement, with no further contributions. Enter your ages, target spending, expected real return and withdrawal rate to get your Coast Number, plus how your current portfolio compares.
Coast FIRE Calculator
What you need invested today to coast to retirement
In today's dollars
After inflation, usually 5–7
4% = a 25× target
Coast number: $162,632 · target $1,250,000 in 35 years
Results
Coast FIRE Number
$162,632
needed invested today
Retirement Target
$1,250,000
at age 65
Path to Coast FIRE
The amount you need invested at each age to reach your target by growth alone. Add your portfolio to compare.
If the Return Were Different
Coast Number If You Wait
The coast number is what you would need invested today for growth alone to reach $1,250,000 by age 65. Reaching it does not mean you stop working — it means you could stop contributing to retirement savings and still arrive on target.
Spending is in today's dollars, so the return must be a real return after inflation. Entering a nominal figure such as a 10% historical market average would badly understate the number: over 35 years the gap between 6% real and 10% nominal exceeds $118,000 on a $1.25M target.
Without contributions, your portfolio and the coast number compound at the same rate, so the ratio between them never changes with age. If you are not coasting today you will not drift into it — that is why there is no "date you reach Coast FIRE" here.
The assumed return matters enormously over long horizons. Across 4% to 8%, the coast number for this plan spans $232,226. Treat any single figure as one scenario rather than a prediction.
Step-by-Step Calculation
Retirement Target = Annual Spending ÷ (SWR ÷ 100)
Retirement Target = $50,000 ÷ 0.0400 = $1,250,000
That is the same as 25.00× annual spending, since 1 ÷ 0.0400 = 25.00.
Years to Retirement = 65 − 30 = 35 years
Coast Number = Retirement Target ÷ (1 + return)^Years
(1 + 0.0600)^35 = 7.686087
Coast Number = $1,250,000 ÷ 7.6861 = $162,631.52
Understanding Coast FIRE
Coast FIRE is the milestone where your existing investments will reach your full retirement target on their own, without another dollar contributed. It is a much earlier and more achievable point than full financial independence.
Crucially, it does not mean you stop working. It means retirement saving becomes optional. You still need income to cover living costs, but the pressure to save on top of that disappears — which opens up lower-paid work, part-time hours, or a career change that would otherwise be unaffordable.
The maths is simply a present value. Work out the nest egg you will need, then discount it back to today at your expected return. Everything hinges on the time left to compound, which is why the same target costs $162,632 at age 30 but $521,581 at age 50.
Coast FIRE Formulas
1. Retirement Target
2. Years to Retirement
3. Coast Number
Use a Real Return, Not a Nominal One
This is the single most common way to get a Coast FIRE calculation badly wrong. Because your spending target is in today's dollars, the return must also be in real terms — after inflation. Historic stock market averages of 9% to 10% are nominal figures, and mixing them with today's-dollars spending understates what you need:
| Assumed Return | Type | Coast Number |
|---|---|---|
| 6% | Real — correct | $162,632 |
| 10% | Nominal — wrong here | $44,480 |
A difference of $118,151.39 on the same plan. Either use a real return with today's-dollars spending, or a nominal return with inflated future spending — but never mix the two.
The Withdrawal Rate Sets the Target
Dividing by the withdrawal rate is the same as multiplying by its reciprocal. For $50,000 of annual spending, discounted over 35 years at 6%:
| Withdrawal Rate | Multiple | Retirement Target | Coast Number |
|---|---|---|---|
| 3.0% | 33.33× | $1,666,667 | $216,842 |
| 3.5% | 28.57× | $1,428,571 | $185,865 |
| 4.0% | 25.00× | $1,250,000 | $162,632 |
| 4.5% | 22.22× | $1,111,111 | $144,561 |
| 5.0% | 20.00× | $1,000,000 | $130,105 |
Dropping from 4% to 3% raises the target by $416,667 and the coast number by $54,210.51 — the small gap against subtracting the rounded rows above is just rounding. Lower rates buy safety against a bad sequence of returns, at the cost of needing substantially more.
How Much the Return Assumption Matters
Over 35 years, small differences in the assumed return compound into very large differences in the coast number. For the Example 1 plan:
| Real Return | Coast Number | vs 6% |
|---|---|---|
| 4% | $316,769 | +$154,137.82 |
| 5% | $226,613 | +$63,981.33 |
| 6% | $162,632 | — |
| 7% | $117,079 | −$45,552.85 |
| 8% | $84,543 | −$78,088.34 |
A spread of $232,226.16 across a plausible range of assumptions. Anyone quoting a single precise coast number is overstating the precision available.
Why There Is No "Date You Reach Coast FIRE"
A natural question is when your portfolio will catch up to the coast number. Without contributions, it never does — and the reason is worth seeing. Your portfolio grows at (1+r)^(A−A₀), while the coast number grows at (1+r)^(R−A). Their ratio is:
Both sides compound at the same rate, so the ratio is constant at every age. Someone with $100,000 at 30 against a $1.25M target at 6%:
| Age | Coast Number | Portfolio | Ratio |
|---|---|---|---|
| 30 | $162,632 | $100,000 | 0.614887 |
| 40 | $291,248 | $179,085 | 0.614887 |
| 50 | $521,581 | $320,714 | 0.614887 |
| 60 | $934,073 | $574,349 | 0.614887 |
| 65 | $1,250,000 | $768,609 | 0.614887 |
Identical to six decimal places at every age. If you are at 61% today, you will still be at 61% in thirty years. Closing the gap requires contributions — growth alone will not do it.
The Cost of Starting Later
The same $1.25M target at 65, seen from different starting ages:
| Starting Age | Years to Compound | Coast Number |
|---|---|---|
| 25 | 40 | $121,528 |
| 30 | 35 | $162,632 |
| 35 | 30 | $217,638 |
| 40 | 25 | $291,248 |
| 45 | 20 | $389,756 |
| 50 | 15 | $521,581 |
| 55 | 10 | $697,993 |
| 60 | 5 | $934,073 |
Waiting from 30 to 40 nearly doubles the requirement, from $162,632 to $291,248. The ten years of compounding you give up are worth more than anything you are likely to save in the meantime.
Benefits of Using the Coast FIRE Calculator
Example Calculations
Three plans worked through step by step, all at a 4% withdrawal rate:
Example Scenario 1 — Age 30, Retiring at 65
Annual spending $50,000, 4% withdrawal rate, 6% real return.
Retirement Target = $50,000 ÷ 0.04 = $1,250,000
That is the same as 25× annual spending, since 1 ÷ 0.04 = 25
Years to Retirement = 65 − 30 = 35
(1.06)^35 = 7.686087
Coast Number = $1,250,000 ÷ 7.686087 = $162,632
Result: $162,632 invested today grows to $1.25M by 65 with no further contributions
Example Scenario 2 — Age 40, Retiring at 60
Annual spending $60,000, 4% withdrawal rate, 5% real return.
Retirement Target = $60,000 ÷ 0.04 = $1,500,000
Years to Retirement = 60 − 40 = 20
(1.05)^20 = 2.653298
Coast Number = $1,500,000 ÷ 2.653298 = $565,334
The shorter horizon is what drives the higher figure — just 20 years of compounding
Result: $565,334 needed today, versus $162,632 in Example 1
Example Scenario 3 — Age 35, Retiring at 65
Annual spending $40,000, 4% withdrawal rate, 7% real return.
Retirement Target = $40,000 ÷ 0.04 = $1,000,000
Years to Retirement = 65 − 35 = 30
(1.07)^30 = 7.612255
Coast Number = $1,000,000 ÷ 7.612255 = $131,367
Lower spending and a higher return both pull the number down
Result: $131,367 invested today reaches $1M by 65
What This Model Leaves Out
The calculation assumes a steady real return every single year, which no market delivers. Sequence of returns matters a great deal: the same average arriving as a bad first decade behaves very differently from one that arrives smoothly, and that risk is highest near retirement. The model also ignores tax on withdrawals, investment fees, Social Security or pension income, and any change to your spending plans — all of which can move the answer substantially. On the other side, the 4% rule itself comes from studies of 30-year retirements; a longer horizon argues for a lower rate. Treat the coast number as a useful checkpoint that tells you whether saving is still urgent, not as a precise forecast. This is general information, not financial advice.
Frequently Asked Questions
- What is Coast FIRE?
- Coast FIRE is the point where your existing investments will grow to your full retirement target on their own, with no further contributions. It does not mean you stop working — it means retirement saving becomes optional, and anything you earn from then on can go toward living rather than the future.
- How do you calculate a Coast FIRE number?
- Work out your retirement target by dividing annual spending by your withdrawal rate, then discount it back to today at your expected return. For $50,000 a year at 4%, the target is $1,250,000; discounted over 35 years at 6% that is $1,250,000 ÷ 1.06^35 = $162,632.
- Why is 4% the same as 25 times spending?
- Because dividing by 0.04 is the same as multiplying by 25. A 3.5% rate gives a 28.57× multiple and 3% gives 33.33×, so lower withdrawal rates require noticeably larger portfolios — $1.67M rather than $1.25M on $50,000 of spending.
- Should I use a real or nominal return?
- A real return, after inflation — usually 5% to 7% for a stock-heavy portfolio. This matters enormously. Entering a 10% nominal figure alongside spending in today's dollars would give $44,480 instead of $162,632, understating what you need by over $118,000.
- When will I reach Coast FIRE if I am not there yet?
- Not through growth alone. Without contributions your portfolio and the coast number compound at exactly the same rate, so the ratio between them never changes with age — the algebra cancels the age term entirely. If you are at 61% today you will still be at 61% in twenty years. Closing the gap requires contributions.
- How much difference does the return assumption make?
- A great deal over long horizons. On the Example 1 plan the coast number ranges from $316,769 at a 4% return down to $84,543 at 8% — a spread of $232,226 from the same spending target. Treat any single figure as one scenario rather than a forecast.
- What happens if I wait a few years?
- The number rises sharply, because there is less time to compound. On the Example 1 plan, waiting from 30 to 40 raises the coast number from $162,632 to $291,248, and waiting until 50 raises it to $521,581. Every year of delay costs roughly the annual growth rate.
- Is Coast FIRE different from regular FIRE?
- Yes. Full FIRE means having the whole nest egg now and being able to stop working entirely. Coast FIRE is a much earlier milestone — you still need income to cover living costs, but you no longer need to save for retirement on top of that.
- Does this account for Social Security or a pension?
- No. Any guaranteed income in retirement reduces how much your portfolio needs to cover, so the target here is conservative if you expect Social Security or a pension. You could subtract that expected income from your annual spending before calculating.
- How reliable is this projection?
- It assumes a steady real return every year, which no market delivers. Sequence of returns matters — a bad decade early behaves very differently from the same average arriving smoothly — and the model ignores tax, fees and changes to your plans. It is a useful checkpoint, not a guarantee.