Coast FIRE is the moment you realize you don't have to save another dollar for retirement — not because you're rich, but because the money you've already invested has enough runway left to compound into a full retirement on its own. You still work. You still pay the bills. You just stop feeding the retirement accounts, because time and compound growth are doing that job for you now.
This guide covers what Coast FIRE actually means, the math behind the number, how it compares to other FIRE variants, and what to watch out for if you're aiming for it.
What Coast FIRE actually means
Traditional retirement planning asks: "How much do I need saved by the time I stop working?" Coast FIRE asks a different question: "How much do I need saved right now so that, left untouched, it grows into that same number by the time I retire?"
Once your invested balance passes that number, continued contributions become optional. You can keep saving to retire earlier or more comfortably, but you no longer need to. That flexibility is the entire point — it opens the door to taking a lower-stress job, cutting back to part-time, switching careers, or simply keeping your current job without the anxiety of falling behind.
The tradeoff is that Coast FIRE doesn't mean you stop working. You still need income to cover current living expenses; you've just decoupled "saving for the future" from "paying for today."
The Coast FIRE formula
The math is a straightforward present-value calculation:
Coast FIRE number = Retirement target ÷ (1 + r)^n
- Retirement target is the total portfolio you'll need at retirement age (commonly estimated using the 25x rule — 25 times your expected annual retirement spending, based on a roughly 4% initial withdrawal rate).
- r is your assumed annual real (inflation-adjusted) rate of return, often estimated around 6-7% for a diversified stock-heavy portfolio.
- n is the number of years between now and your target retirement age.
Worked example: age 30
Say you're 30, plan to retire at 65 (35 years out), want to spend $80,000 a year in retirement, and assume a 7% real return. Using the 25x rule, your retirement target is $80,000 × 25 = $2,000,000.
Coast FIRE number = $2,000,000 ÷ (1.07)^35 ≈ $187,000
If you already have $187,000 invested at 30, you've hit Coast FIRE — assuming you never add another dollar and the market delivers that average return over the next 35 years.
Worked example: age 40
Same target and return assumption, but now with only 25 years to retirement:
Coast FIRE number = $2,000,000 ÷ (1.07)^25 ≈ $368,500
Notice the number roughly doubles for ten fewer years — that's the cost of losing a decade of compounding. The earlier you start, the smaller the number you need to hit, which is why Coast FIRE is discussed so often as a young-professional strategy. You can run your own numbers, adjust the return assumption, and see how contribution timing changes the outcome with the Coast FIRE Calculator.
Coast FIRE vs. FIRE, Lean FIRE, and Barista FIRE
FIRE has splintered into several variants, and it's easy to conflate them:
- Standard FIRE: Save aggressively until your full portfolio covers all future living expenses, then stop working entirely.
- Lean FIRE: A version of standard FIRE built around a minimal, stripped-down budget — a smaller annual spend means a smaller total number, but a tighter lifestyle in retirement.
- Fat FIRE: The opposite of Lean FIRE — a larger target portfolio that supports a more comfortable or upscale retirement spend.
- Barista FIRE: You leave your career for lower-stress, often part-time work that covers current expenses and sometimes benefits like health insurance, while your existing retirement savings keep compounding untouched.
- Coast FIRE: You've saved enough that your retirement accounts no longer need contributions, but you still work full-time (or close to it) to cover today's expenses.
Coast FIRE and Barista FIRE overlap conceptually — both let your existing savings coast — but Barista FIRE usually implies a specific career downshift, while Coast FIRE is just the funding milestone itself. You can be "Coast FIRE'd" and still work your current job full-time; what changes is that saving more becomes a choice, not a requirement.
Common mistakes to avoid
Using an unrealistic return assumption. A small change in your assumed rate of return produces a large change in your Coast FIRE number, since it compounds over decades. Using 10% because "that's what the stock market has historically returned" (a nominal, not inflation-adjusted, figure) will understate what you actually need. Stick to a real-return assumption, and consider running the numbers at more than one rate to see a range.
Ignoring the withdrawal-rate debate. The 25x rule rests on the classic 4% safe withdrawal rate. It's a reasonable starting point, but plenty of current research argues for a somewhat more conservative rate for a retirement that could last 30+ years — some analysts land closer to 3.5%, which pushes your retirement target (and therefore your Coast FIRE number) higher. Treat 25x as a floor to test, not a guarantee.
Forgetting healthcare and big one-time costs. A Coast FIRE plan built purely on investment growth can get derailed by a health event, a home repair, or supporting a family member. Build a buffer, and don't treat your invested balance as fully spoken for the moment it crosses your Coast FIRE line.
Confusing "coast" with "stop planning." Hitting your number doesn't mean you should ignore your accounts. Keep an eye on asset allocation, rebalance periodically, and revisit your target if your desired retirement age, spending, or lifestyle changes.
Building toward your number faster
The two levers that move your Coast FIRE date are contribution size and time. Because the formula divides by a compounding factor that grows exponentially with years, front-loading contributions in your 20s and 30s has an outsized effect compared to the same dollars invested a decade later. Modeling that effect — what an extra $500 a month today does to your timeline versus the same amount starting five years from now — is exactly what the Compound Interest Calculator is built for.
Once you're closer to your target, it's worth zooming out from the Coast FIRE number itself and stress-testing your full retirement plan — contribution mix across account types, expected Social Security, and drawdown order — with the Retirement Planning Calculator.
Frequently asked questions
Does Coast FIRE mean I never save for retirement again?
Not exactly — it means further retirement contributions become optional rather than required to hit your target. Many people who reach Coast FIRE keep contributing at a reduced rate to retire earlier, build in a safety margin, or pursue Fat FIRE instead of a standard target.
What rate of return should I use to calculate my Coast FIRE number?
Most calculators default to a real (inflation-adjusted) return somewhere in the 5-7% range for a diversified, stock-heavy portfolio, based on long-run historical averages. Because the result is sensitive to this assumption, it's worth calculating your number at a couple of different rates rather than relying on a single estimate.
Is Coast FIRE only realistic for high earners?
High income helps you reach the number faster, but Coast FIRE is really a function of time and savings rate, not income alone. Someone who starts investing consistently in their early 20s needs a smaller Coast FIRE number than someone starting in their late 30s, even at a lower income, simply because they have more years for compounding to do the work.
How is Coast FIRE different from Barista FIRE?
Coast FIRE describes the funding milestone — your retirement savings no longer need new contributions. Barista FIRE usually describes a specific lifestyle choice built on top of that milestone: leaving a full-time career for part-time or lower-stress work, sometimes chosen for benefits like employer health insurance.
What if I want to retire earlier than 65?
Use your actual target retirement age as "n" in the formula. A shorter timeline means less time to compound, so your Coast FIRE number will be higher than it would be for a traditional retirement age — you'd need a larger balance today to coast to an earlier finish line.
Disclaimer
This guide is for general educational purposes only and does not constitute personalized financial, tax, or legal advice. Every reader's situation is different — consult a licensed financial advisor, accountant, or attorney before making decisions based on this content. Figures and rules cited here reflect the most recent information available at time of publication and may change; verify current limits and regulations before acting.