Coast FIRE
Guide · By Kevin Lan · Updated September 2026
Coast FIRE is the milestone where you can stop contributing and still retire on time. Your existing investments coast the rest of the way on compounding alone.
What Coast FIRE means
Coast FIRE is the point where the money you have already invested will grow to your full FIRE number by your target retirement age with no further contributions. Once you reach it, you still need income to cover your day-to-day expenses, but you no longer have to save for retirement. Every dollar already invested keeps compounding toward the finish line on its own.
It is the earliest of the FIRE milestones to reach, because it asks for a fraction of the full number and then lets time do the rest.
The Coast FIRE formula
The coast number is your FIRE number discounted back to today by your expected real return:
Coast number = FIRE number ÷ (1 + real return)years to retirement
For a $1,250,000 FIRE number, a 5% real (after-inflation) return, and 30 years to go, the coast number is $1,250,000 ÷ 1.0530 ≈ $289,000. Invest roughly that much and stop, and if your return assumption holds, it grows to $1.25M in 30 years without another dollar added.
Coast numbers by age: a worked example
Because the number is discounted over the years remaining, it rises the closer you are to retirement. Aiming for a $1,250,000 FIRE number by age 65 at a 5% real return, the amount you need invested today to coast is roughly:
- Age 25 (40 years to grow): about $178,000
- Age 35 (30 years): about $289,000
- Age 45 (20 years): about $471,000
- Age 55 (10 years): about $767,000
The earlier you fund it, the less you need. A 25-year-old who reaches $178,000 and never saves another cent for retirement is, on these assumptions, already coasting to $1.25M.
Why compounding does the rest
Coast FIRE works because growth compounds on a base you have already built, and the later years contribute the most. Over a long horizon, the return earned on prior returns eventually dwarfs new contributions. That is why, past a certain point, saving more barely moves the date while staying invested does. Coast FIRE is simply the balance at which that hand-off is complete: your existing portfolio, left alone, is projected to reach the target.
What Coast FIRE does not cover
It is a milestone, not full independence, and it rests on assumptions worth stating plainly:
- You still have to fund current expenses. Coasting frees you from retirement saving, not from earning a living until you retire. That includes health insurance, which in the U.S. is often the hardest gap to bridge before Medicare age.
- It assumes your real return actually materializes. Long-run U.S. stock returns have averaged roughly 7% real historically, but any single multi-decade stretch can land above or below that. A more cautious return assumption raises the coast number.
- A weak decade near the end still matters. Poor returns just before your target date, when the balance is largest, can leave you short. It is the same sequence-of-returns risk that shapes withdrawal planning. Coasting is not a guarantee; it is a well-founded projection.
Your coast number is a moving target
The coast number rises every year you wait, because each year closer to your target age leaves one fewer year of compounding. So the date you reach Coast FIRE is not the date your balance passes today's coast number. It is the date your balance catches the rising one.
An example: at 32 with $50,000 invested, adding $24,000 a year at a 7% real return, and aiming for $1,250,000 by 65, today's coast number is about $134,000. Your balance passes that in under three years, but by then the coast number has risen. You actually catch it about 4 years and 2 months out, at roughly $178,000. A calculator that compares your balance to today's figure dates Coast FIRE more than a year too early.
How the calculator and app compute it
The calculator below solves for that crossing: it projects your balance with your contributions and finds the first point where it meets the coast number for that date. It reports the coast number you will need then, alongside today's figure. The iPhone app uses the same math (updated in version 1.3), and turns the date into a home-screen countdown to the day you can stop saving, which moves as your investments do.
The calculator also draws the result as a chart. With Coast FIRE selected it shows two lines against your age. For the example above, the dashed coast number starts at about $134,000 at 32 and climbs to the full $1,250,000 at 65. Your balance starts lower, at $50,000, but rises faster because $24,000 a year is still going in. The lines meet about 4 years and 2 months out, at $177,571: that point is your Coast FIRE date. After it, the balance needs no new money. Left alone, it grows along the coast line and reaches $1,250,000 at 65.
References
- Bengen WP. Determining withdrawal rates using historical data. Journal of Financial Planning. 1994;7(4):171–180. The paper that introduced the 4% withdrawal guideline.
- Damodaran A. Historical annual returns on U.S. stocks, bonds and bills (1928–present). NYU Stern School of Business. pages.stern.nyu.edu/~adamodar
- Investopedia. Financial Independence, Retire Early (FIRE): a definition. investopedia.com
- Robin V, Dominguez J. Your Money or Your Life. Revised ed. New York: Penguin Books; 2018. A foundational text of the financial-independence movement.
FIRE calculator
It runs in your browser. Nothing is sent anywhere.
No account, no ads, and we never see your numbers.
Frequently asked questions
How is Coast FIRE different from FIRE?
Full FIRE means your portfolio can cover your expenses now. Coast FIRE means your current portfolio will grow to that amount by your target retirement age without any new contributions, so you can stop saving for retirement, though you still need income to cover living costs until then.
What's the Coast FIRE formula?
Coast number = FIRE number ÷ (1 + real return) raised to the number of years until retirement. It is your FIRE number discounted back to today at your expected after-inflation growth rate.
How much do I need for Coast FIRE at 30?
For a $1,250,000 FIRE number at age 65 and a 5% real return, a 30-year-old needs roughly $227,000 invested to coast, versus about $178,000 at age 25 and $289,000 at 35. Fewer years to grow means a higher coast number; the calculator computes yours from your own figures.
Why does my Coast FIRE number go up every year?
Because it is your FIRE number discounted over the years left until your target age. Each year you get closer, there is one fewer year of growth to count on, so the amount you need invested rises. That is why the date you reach Coast FIRE comes later than the date your balance passes today's coast number.
Can I really stop saving at Coast FIRE?
You can stop saving for retirement; you still need income to cover current expenses until you retire. It's a point of flexibility (part-time work, a lower-paid role, a career break), not full independence.
Is Coast FIRE safe?
It's a projection, not a guarantee. It assumes your expected real return holds over decades, and a poor stretch of returns near your target date can leave you short. Many coasters keep some flexibility, such as a willingness to add savings again if markets underperform.
