How Coast FIRE works
Your income does two jobs over a career: it pays for the life you live now, and it funds the investments that will pay for life after work. Coast FIRE is the point where the second job is done in advance. The money already invested is projected to compound into your FI number by your chosen retirement age, even if you never add another dollar.
From then on, your paycheck only has to cover current spending. You can take a lower-paid role you enjoy, cut to four days a week or start a business, as long as earnings cover the bills and the invested money stays untouched. That is the difference from full FIRE, where the portfolio already covers everything and work is optional today.
Coast FIRE runs on compound growth, so time is the main ingredient. The same target needs far less money at 30 than at 50, because a 30-year-old’s savings have decades more to grow. That growth is an assumption, not a promise, which is why the number deserves a margin and a yearly check.
How to calculate your Coast FIRE number
The calculation runs backward from retirement. First work out what the portfolio must hold on your retirement date, then shrink that figure by the growth you expect between now and then.
Keep every figure at today’s prices. If retirement spending is stated at today’s prices, the growth rate must be a real return, meaning the return after inflation and after fund fees. Mixing today’s-dollar spending with a nominal return that still includes inflation is a common way to understate your number.
- Estimate yearly retirement spending at today’s prices.
- Subtract dependable income, such as Social Security or a pension, to find the gap the portfolio must fill.
- Multiply the gap by 25, the Rule of 25 behind a 4% withdrawal rate, or divide it by the rate you prefer.
- Count the years until your planned retirement date.
- Divide the result by (1 + real return) raised to that number of years.
Coast FIRE vs. Barista FIRE, Slow FI and full FIRE
The FIRE variants differ mainly in when paid work stops and what it pays for. With Coast FIRE you keep working, earnings cover all of today’s spending, and the portfolio grows untouched until a traditional retirement age.
Barista FIRE comes later on the same road: you have left your main career, the portfolio already pays part of your spending, and part-time pay covers the rest. Slow FI is looser than Coast FIRE: you ease off before the portfolio can coast, but keep saving toward independence at a slower pace. Mullet FIRE is a plan for the retirement years themselves: lean at first, fuller spending later.
One way to hold them together: Coast FIRE frees you from saving, Barista FIRE frees you from full-time work, and full FIRE frees you from needing paid work at all.
Common Coast FIRE mistakes
Most Coast FIRE errors make the number look smaller than it is, and they tend to surface only when it is too late to save more. One quirk works in your favor: while you neither add nor withdraw money, the order of good and bad years does not change the ending balance, because only the compound average return matters. A crash in year two and one in year twenty cost the same. Sequence-of-returns risk arrives later, once withdrawals start.
- Using a nominal return, such as 8%, against spending stated at today’s prices.
- Forgetting fees and the income tax due on withdrawals from tax-deferred accounts, both of which raise the balance you need.
- Counting money that will be spent before retirement, such as a home down payment, as coasting money.
- Leaving out Social Security, which inflates the target, or assuming a benefit larger than your own statement shows.
- Dropping contributions below the level that captures a 401(k) match, which gives up money your employer would add.
- Treating the calculation as one-and-done instead of rechecking it every year.
Coast FIRE pros, cons and how to add margin
The upside is choice before you reach the full finish line. People use Coast FIRE to change careers, work part-time while children are young, or trade pay for better hours, knowing retirement is already funded on paper.
The downside is that the paper can be wrong. A decade of weak returns, higher fees or a larger retirement budget can leave the portfolio short, and the later you spot the gap, the fewer working years you have to close it. Because you stopped saving, no new money is buying investments cheaply during a downturn either.
To add margin, coast only after passing the number comfortably, keep contributing a smaller sum, assume a lower real return, or plan to work a few years past the date in the formula. Rechecking the projection each year turns a single guess into a course you can correct.
Illustrative numbers
Coast FIRE number for a 35-year-old retiring at 65
- FI number
- What the portfolio must hold at retirement, at today’s prices: the yearly spending gap × 25 under the 4% rule
- r
- Expected yearly real return, after inflation and fees
- n
- Years until your planned retirement date
The result is a projection that assumes a steady average return; real markets vary, so many people add a margin.
Retirement spending, today’s dollars$60,000 a year
Social Security estimate, today’s dollars$24,000 a year
Gap the portfolio must cover$36,000 a year
FI number (25 × gap)$900,000
Growth over 30 years at a 5% real return× 4.32
Coast FIRE number ($900,000 ÷ 4.32)about $208,000
With about $208,000 invested today and no new contributions, the portfolio is projected to reach $900,000 at today’s prices by 65 if it earns 5% a year after inflation. Leave out the Social Security estimate and the target becomes $1.5 million, with a Coast number near $347,000.
At a glance
Coast FIRE number per $1 million of FI number, by years to retirement and real return
| Years until retirement | 3% real return | 5% real return | 7% real return |
|---|---|---|---|
| 10 | $744,000 | $614,000 | $508,000 |
| 15 | $642,000 | $481,000 | $362,000 |
| 20 | $554,000 | $377,000 | $258,000 |
| 25 | $478,000 | $295,000 | $184,000 |
| 30 | $412,000 | $231,000 | $131,000 |
| 35 | $355,000 | $181,000 | $94,000 |
Put it in your plan
Coast FIRE in MoneyWhatIf
To test Coast FIRE in MoneyWhatIf, start a What-If, stop or cut your contributions and keep your retirement date. The edited plan projects again with the previous projection drawn dashed underneath, so you can see whether the balance still funds retirement spending. A life milestone with a net-worth target equal to your FI number, at today’s prices, marks the first year the coasting plan gets there. While the edit is open, the Wellness scorecard shows how your financial independence card moved, and Plan Resilience reruns the plan across 100, 300 or 500 reshuffled historical market paths.
Common questions
Coast FIRE FAQs
How much do you need for Coast FIRE at 30?
It depends on your FI number and how long the money can grow. Retiring at 65, a 30-year-old has 35 years: at a 5% real return, each $1 million of FI number needs about $181,000 invested today. At 40, with 25 years to go, it takes about $295,000 per $1 million, and at 50 about $481,000. That is why reaching Coast FIRE early in a career takes far less money.
Should I stop contributing to my 401(k) once I hit Coast FIRE?
Not necessarily. Coast FIRE says you could stop, not that you should. Pre-tax contributions still cut this year’s tax bill, an employer match is money you would otherwise leave behind, and extra savings add margin if returns disappoint. For 2026 you can defer up to $24,500 into a 401(k), plus an $8,000 catch-up from age 50 ($11,250 at ages 60–63), so even a partial contribution can matter.
Does Coast FIRE account for Social Security?
It should. Subtract the benefit you expect from your retirement spending before multiplying by 25, using the estimate on your Social Security statement at today’s prices. SSA estimated the average retired-worker benefit at $2,071 a month in January 2026, about $24,850 a year. Ignoring a benefit that size would overstate the FI number by about $620,000. Some people count only part of their estimate to add margin.
Can you use Coast FIRE to retire early?
Yes, but it takes more money. Set the years in the formula to your early retirement date: fewer years of growth mean a larger Coast number. Two gaps also appear. Money in a 401(k) or IRA generally owes a 10% additional tax if withdrawn before 59½, and Social Security retirement benefits cannot start before 62, so the portfolio must cover the whole budget until benefits begin, with part of it somewhere you can reach early, such as a taxable brokerage account.