Coast FIRE Calculator

How do you use this Coast FIRE calculator?

1. Enter your age, the age you want to fully retire, and what you have invested for retirement today: 401(k), IRA, HSA and taxable brokerage accounts, but not your home or emergency fund.
2. Enter how much you expect to spend each year in retirement, in today's dollars, and what you invest each month now. Spending should include taxes and health insurance.
3. Optionally add Social Security or a pension. If you are planning together, turn on Plan as a couple and add your partner's age and benefit.
4. Check the return, inflation, fees and withdrawal rate under Assumptions. The defaults are explained below.

Results update as you type. The headline figure is your Coast FIRE number for today. Underneath, the Coast FIRE age is when you'll reach it if you keep investing at your current rate, which makes this a Coast FIRE age calculator as well. The If you stop investing today card works the other way round: it shows what your current balance grows to and the earliest age it could retire you on its own, so you can use it as a coast retirement calculator once you have stopped contributing. Copy the share link to save your scenario, or download the year-by-year projection as a CSV.

How do you calculate a Coast FIRE number?

Whether you call it Coast FIRE, Coast FI or CoastFI (and it is sometimes misspelled cost FIRE), the calculation has four steps. Your Coast FIRE number is your retirement target, discounted back to today at your expected real return.

1. Pick your retirement spending in today's dollars, including taxes and health insurance.
2. Turn it into a FIRE number. With flat spending and no other income, the target is spending ÷ safe withdrawal rate. At 4% that is 25 times your spending, the target used across the FIRE movement^[1] and based on William Bengen's 1994 research^[2].
3. Convert your expected return to a real return with the Fisher equation: (1 + return − fees) ÷ (1 + inflation) − 1. A 7% return with 0.1% fees and 3% inflation gives 3.79%.
4. Discount the FIRE number back to today. Money growing at a real return r for n years multiplies by (1 + r)ⁿ. You want today's balance × (1 + r)ⁿ to equal the FIRE number, so:

Coast FIRE number = FIRE number ÷ (1 + real return)^{years until retirement}

To calculate Coast FI in a spreadsheet, put your FIRE number in A1, the real return in A2 and the years until retirement in A3, then enter =A1/(1+A2)^A3. A useful shortcut: at 3.8% real, money doubles about every 19 years, so every 19 years of extra head start roughly halves the number you need.

Worked example

Alex is 30, wants to retire at 60, and plans to spend $50,000 a year. With a 7% expected return, 3% inflation and 0.1% fees, the real return is 3.79%.

• FIRE number: $50,000 ÷ 4% = $1,250,000
• Coast FIRE number: $1,250,000 ÷ (1.0379)³⁰ = $409,917

If Alex has $409,917 invested at 30, they could stop saving for retirement entirely and, if returns match the assumption, have $1,250,000 at 60. Social Security and pensions make step 2 a little more involved, because the portfolio only has to cover the gap after those benefits start. The calculator does this year by year, as shown further down.

What is my Coast FIRE number at each age?

The table gives the Coast FIRE number by age for every $10,000 of yearly retirement spending, retiring at 65 with a 4% withdrawal rate. Multiply by your spending in tens of thousands: if you plan to spend $60,000, multiply by 6. Read across to see how much the return assumption matters.

Our calculation, today's dollars, no Social Security or pension. Two patterns stand out. Waiting from 30 to 40 raises the number by about 45% at the default return, and the return assumption matters more the younger you are: at 25, the 3% column is 3.2 times the 6% column. The calculator shows the same grid for your own target under the chart.

Which inputs change the answer most?

Everything is calculated in today's dollars. Here is what the defaults are based on, and how much each one moves Alex's $409,917 coast number.

• Return: 7% default. The S&P 500 returned 10.0% a year from 1928 to 2025^[3], but Vanguard's current 10-year forecast for US stocks is 4.8%-6.8%^[4]. A 7% default sits between history and forecasts. One percentage point more real return lowers Alex's number to $307,441; one point less raises it to $548,074.
• Inflation: 3% default. US inflation averaged about 3% a year from 1928 to 2025^[3], and was 3.7% in the 12 months to September 2026^[5].
• Fees: 0.1% default. Fees come straight off the return. At 1% a year in fund and advisory fees, the real return falls to 2.91% and Alex would need $528,264.
• Withdrawal rate: 4% default. 4% was designed for 30-year retirements. If you will retire early and need the money to last 50 to 60 years, research suggests 3.25%-3.5% is safer^[6]. At 3.5%, Alex's coast number rises to $468,476.
• Plan until age: 95 default. This sets how long the money has to last. With Social Security or a pension it changes the target, because the portfolio covers the gap for more or fewer years.
• Stocks in your portfolio: 80% default. This only affects the risk tests, which replay history for your stock and bond mix.

See the full methodology for timing conventions and how the risk tests work.

How does a Coast FIRE calculator with Social Security work?

Social Security usually lowers your Coast FIRE number a lot, because every dollar of lifetime, inflation-adjusted benefit is a dollar your portfolio does not have to pay. Turn on Social Security in the calculator and enter your estimated benefit and claiming age. The calculator then works through retirement year by year: it funds your full spending from the portfolio until benefits start, and only the gap afterwards.

In Alex's example, adding a $24,000 benefit from 67 lowers the FIRE number from $1,250,000 to $807,824 and the Coast FIRE number from $409,917 to $264,912. The seven years from 60 to 67 still need the full $50,000, which is why the target doesn't fall by the whole value of the benefit.

Your claiming age matters too. Full retirement age is 67 for anyone born in 1960 or later; claiming at 62 cuts the benefit by 30% and waiting until 70 adds 24%^[7]. For Alex, claiming a reduced benefit at 62 gives a coast number of $283,088, and waiting until 70 gives $254,840. If you worry about future benefit cuts, use the Share of benefit to count on setting: counting 75% of Alex's benefit gives $301,163.

Get your personal estimate from the Social Security Administration^[8]. Keep in mind that your benefit is based on your highest 35 years of wage-indexed earnings, and missing years count as zero^[9]. If coasting means much lower pay or years out of work, a benefit estimate that assumes your current salary may be too high, so enter a lower figure.

What about a pension?

A pension works the same way. Turn on Include a pension and enter the yearly amount and start age. If Alex had a $12,000 pension starting at 60, the FIRE number would fall to $950,000 and the coast number to $311,537. Enter the amount in today's dollars; if the pension has no cost-of-living adjustment, enter a lower figure, because inflation will shrink what it buys.

How do you use the Coast FIRE calculator for couples?

Couples share one portfolio and one budget, but usually have two ages and two Social Security benefits that start at different times. Turn on Plan as a couple and enter your combined invested assets, combined monthly investing and combined retirement spending, plus your own age and benefit. Then add your partner's age, benefit and claiming age. The calculator places your partner's benefit on your timeline and keeps the plan running until the younger of you reaches the “Plan until” age.

Take Sam, 35, and Jo, 32. They want to stop working when Sam is 62 and spend $70,000 a year. Sam expects $26,000 a year from Social Security at 67; Jo expects $16,000 at 67, which is when Sam is 70. The plan runs until Jo is 95, so Sam's age 98.

• Without Social Security, their Coast FIRE number is $641,572.
• With both benefits on the right dates, it is $345,675.
• The common shortcut of starting both benefits at “67” and planning to 95 for the older partner gives $330,876, which understates what they need by $14,799.

Two more rules matter for couples. A partner with a small earnings record can receive up to 50% of the other partner's full benefit as a spousal benefit at full retirement age, so enter whichever is higher. And when one partner dies, the survivor generally keeps the higher of the two benefits rather than both^[7]. The calculator counts both benefits for the whole plan, so if your benefits are similar in size, a lower share of benefit to count on is a sensible cushion.

How do you read the Coast FIRE chart?

The chart under your results plots three things in today's dollars. The shaded area is your projected portfolio, assuming you keep investing until you reach Coast FIRE and then stop. The rising line is your Coast FIRE number at each age: it grows by your real return every year, because each year you wait leaves one less year of compounding. The dashed line is your FIRE number.

The point where the portfolio climbs above the coast line is your Coast FIRE age. From there the portfolio grows on its own and should meet the dashed line at your retirement age. After that it starts paying for your retirement, and the table view lists each year's withdrawal and other income.

What if returns are lower than the calculator assumes?

The coast number assumes you earn exactly your expected return every year until you retire. Suppose Alex starts coasting at 30 with exactly $409,917, but the real return turns out 0.5, 1 or 2 percentage points lower than the 3.79% assumed. Here is where Alex lands at 60, and what each fix would take on its own.

Our calculation: target $1,250,000, $50,000 spending, 4% withdrawal rate. “Or retire at” is the earliest full retirement age with no more contributions. “Or add yearly” is what Alex would need to keep investing every year from 30 to 60 to hit the target anyway. “Or spend” is the yearly spending the smaller balance supports from 60.

One percentage point of lower return over 30 years leaves Alex with 75% of the target. Small, steady contributions fix that far more cheaply than delaying retirement: $6,855 a year does the same job as working until 71. That is the case for keeping a little investing going after you hit your number.

Real markets don't deliver a steady return, and a bad decade right after you retire does the most damage, because the returns early in retirement largely decide how much you can safely spend^[10]. The calculator's risk section replays your plan through 2,000 simulated market histories and through every actual retirement start year since 1928, so you can see how often it would have come up short and by when.

How do you check you're still on track each year?

Once you start coasting, do a quick check once a year. Note your age and the balance of the same accounts you entered at the start. Enter both in the calculator, or simply grow last year's coast number by your real return. If your balance is at or above the new number, you're still coasting. If it's below, you have three levers: invest a lump sum, restart contributions for a while, or plan to retire later.

Say Alex coasts from 30 with exactly $409,917, and the first year is bad: the portfolio falls 20% after inflation, to $327,933. At 31 the coast number has risen to $425,438, so Alex is at 77% of it. To get back on track, Alex could:

• invest $97,504 at once;
• invest $10,000 a year for about 13 years;
• or do nothing and plan to fully retire at 68 instead of 60.

A good year later may undo some of the damage, but the plan already assumes average returns, so don't count on it. Starting to coast with a cushion above your number, and re-running the numbers after any big change in spending or plans, keeps these checks boring.

What mistakes should you avoid with a Coast FIRE calculator?

• Using a nominal return with today's spending. Plugging in 7% as if it were real growth gives Alex a coast number of $164,209 instead of $409,917. Spending in today's dollars needs an after-inflation return.
• Counting money that isn't invested for retirement. Home equity and your emergency fund don't compound toward your target, and you may need the emergency fund while you coast.
• Leaving out taxes and health insurance. Retirement spending should be what you'll actually pay, including tax on traditional 401(k) and IRA withdrawals and insurance premiums before Medicare.
• Using 4% for a very long retirement. If the money has to last 50 years or more, a lower withdrawal rate is safer^[6], and it raises the coast number.
• Forgetting when the money is available. If you plan to retire before 59½, most withdrawals from 401(k)s and IRAs face a 10% additional tax unless an exception applies^[11]. The early retirement calculator checks whether your accessible accounts can bridge that gap.
• Treating the number as fixed. Your coast number rises every year you don't reach it, and moves whenever your spending or retirement age changes. Re-check it yearly.

How does Coast FIRE compare with other types of FIRE?

Coast FIRE needs the smallest portfolio of any FIRE path, because you keep working to pay today's bills and only stop saving. The table sums up the main types. For the trade-offs between the two part-way options, read Coast FIRE vs Barista FIRE; for the concept and whether it suits you, see what Coast FIRE is; and for the full movement, start with what FIRE is.