Coast FIRE is one of the fastest-growing ideas in the early retirement community — and unlike traditional FIRE, it doesn’t require living like a monk or retiring at 35. Here’s what it actually means, how to calculate your own Coast FIRE number, and why it’s become such a popular middle-ground goal.
What Does Coast FIRE Mean?
Coast FIRE (Financial Independence, Retire Early) describes a specific milestone: the point at which you’ve invested enough that, without contributing another dollar, compound growth alone will carry your investments to a full retirement number by a traditional retirement age.
Once you hit your Coast FIRE number, you can theoretically stop saving for retirement entirely and simply cover your current living expenses — “coasting” on the growth already in motion — while your investments compound in the background untouched.
This is different from full FIRE, where the goal is to have enough invested to retire immediately. Coast FIRE is about reaching a point where retirement is already funded for later, even if you keep working and earning for years to come.
Why Coast FIRE Has Become So Popular
Traditional FIRE requires extreme savings rates (often 50%+) sustained for a decade or more, and full early retirement in your 30s or 40s. Many people find that unrealistic or undesirable — they don’t necessarily want to stop working entirely, they just want the pressure of retirement saving lifted.
Coast FIRE offers that: once you hit the number, you can shift focus toward lower-paying but more fulfilling work, part-time hours, or simply stop stressing about maxing out retirement accounts every year, because the math already works out for your future.
How to Calculate Your Coast FIRE Number
Step 1: Determine your target retirement number Use the common rule of thumb: annual retirement expenses × 25 (based on a 4% safe withdrawal rate).
Example: If you expect to need $50,000/year in retirement, your full retirement target is $1,250,000.
Step 2: Work backward using compound growth Your Coast FIRE number is the amount you need invested today so that, left alone with no further contributions, it grows to your full retirement target by your target retirement age — using an assumed average annual return (commonly 7% after inflation).
The formula:
Coast FIRE Number = Retirement Target ÷ (1 + growth rate)^years remaining
Example: 30-year-old aiming to retire at 65 with a $1,250,000 target
- Years remaining: 35
- Assumed growth rate: 7%
- Coast FIRE number: $1,250,000 ÷ (1.07)^35 ≈ $115,000
This means if this person already has $115,000 invested, they don’t technically need to save another dollar for retirement — 35 years of compound growth alone would carry that amount to $1,250,000, assuming a steady 7% average return.
Example: Same target, but starting at age 40 (25 years remaining)
- Coast FIRE number: $1,250,000 ÷ (1.07)^25 ≈ $228,000
Notice how much higher the required number is with 10 fewer years — this is the core lesson of Coast FIRE: the earlier you hit your number, the smaller it needs to be, because compounding has more time to do the work.
Coast FIRE Numbers by Starting Age (Example: $1,250,000 Target, 7% Growth, Retiring at 65)
| Current Age | Years Remaining | Approximate Coast FIRE Number |
|---|---|---|
| 25 | 40 | $83,500 |
| 30 | 35 | $115,000 |
| 35 | 30 | $164,000 |
| 40 | 25 | $228,000 |
| 45 | 20 | $323,000 |
| 50 | 15 | $453,000 |
What Happens After You Hit Coast FIRE
Reaching your Coast FIRE number doesn’t mean you stop earning or spending on necessities — it means your retirement savings are effectively on autopilot. Common paths people take afterward:
- Continue working full-time, but redirect what used to be retirement contributions toward other goals (a home down payment, kids’ education, travel, or just a more comfortable lifestyle now)
- Shift to lower-stress or lower-paying work they find more fulfilling, since income now only needs to cover current living expenses, not retirement savings on top
- Reduce to part-time hours, using the freed-up time however they choose
- Keep investing anyway as a buffer against a lower-than-expected market return, rather than cutting contributions to zero
Important Caveats to the Coast FIRE Math
- The 7% growth assumption isn’t guaranteed. Real market returns vary significantly year to year — Coast FIRE math works on averages over long periods, not a smooth guaranteed path.
- It typically doesn’t account for healthcare costs before Medicare eligibility if you plan to reduce income significantly before 65 — this needs to be budgeted for separately.
- Inflation matters. The calculations above are generally done in “real” (inflation-adjusted) terms, but it’s worth revisiting your numbers periodically as your actual expenses and market conditions evolve.
- It assumes you stop contributing entirely, which is a planning milestone, not necessarily a recommendation — many people choose to keep contributing even after reaching Coast FIRE as a safety margin.
Frequently Asked Questions
Is Coast FIRE the same as being financially independent? Not quite — Coast FIRE means your retirement is funded for the future, but you still need current income to cover today’s living expenses. Full financial independence (traditional FIRE) means your investments can cover your living expenses right now, without needing to work at all.
What if I don’t hit my Coast FIRE number by a certain age — does that mean I’ve failed? No — it’s a helpful benchmark, not a deadline with consequences. Many people simply keep contributing at a normal pace and reach full retirement savings the traditional way, without ever “coasting.”
Does Coast FIRE work with a lower or higher assumed growth rate? Yes — the formula works with any assumed rate, but a lower rate (say 5-6%) produces a more conservative, higher required Coast FIRE number, while a higher rate (8%+) produces an optimistic, lower number. Many planners recommend using a conservative rate to build in a safety margin.
Do employer 401(k) matches count toward my Coast FIRE number? Yes — any money already invested on your behalf, including vested employer contributions, counts toward your current total when calculating where you stand relative to your Coast FIRE number.
This article is for informational purposes only and does not constitute financial advice. Investment returns are not guaranteed and actual results will vary — consult a licensed financial advisor before making retirement planning decisions.