TL;DR
Coast FIRE is the portfolio level at which compound growth alone — with no further contributions — will reach your full FIRE number by your target retirement age. Typically about 40–60% of full FIRE.
What Coast FIRE actually means
You've hit Coast FIRE when your current portfolio, left untouched and compounded at your assumed real return, will grow into your full FIRE number by your target retirement age.
The math: Coast FIRE number = FIRE number / (1 + real return)^years_to_retirement
For a £1m FIRE target at age 60, with 25 years to go and an assumed 5% real return: £1,000,000 ÷ (1.05)^25 = £295,303.
If you currently have £295k, you can stop saving today and your portfolio will (probably) grow into £1m of purchasing power by age 60. You still need to fund living expenses from elsewhere — Coast FIRE doesn't mean you stop working. It means you stop saving.
Why people pursue it
Coast FIRE is the inflection point where retirement saving is no longer the binding constraint on your life. You can:
- Take a lower-paying but more interesting job because you only need to cover current expenses.
- Reduce hours without delaying retirement.
- Take a sabbatical without sequence-risking your future.
- Change careers without panic.
It's also psychological — knowing the retirement question is solved removes the daily anxiety about saving more, faster.
The numbers across different ages
For a £1m real FIRE target, assuming 5% real returns:
| Current age | Years to 60 | Coast FIRE number | |---|---|---| | 25 | 35 | £181k | | 30 | 30 | £231k | | 35 | 25 | £295k | | 40 | 20 | £377k | | 45 | 15 | £481k | | 50 | 10 | £614k |
The earlier you hit it, the smaller the absolute number — but the harder it is to accumulate that much that young.
The assumptions are doing a lot of work
Two assumptions can blow up Coast FIRE:
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Real return. If you assume 5% real and get 3%, your Coast portfolio grows to about 65% of what you'd planned. Bad sequence years early in the Coast period (when the portfolio is small) hurt much more than late ones.
-
Spending stability. Coast FIRE assumes your future spending matches today's plan. Kids, divorce, healthcare shocks, ambitious house upgrades — any of these can push the target up and undo Coast.
Smart Coast planners assume 4% real return, not 5%, and add a 20% buffer to the calculated number. That's the realistic threshold to stop saving, not just the mathematical minimum.
Coast FIRE vs Barista FIRE vs Full FIRE
- Coast FIRE: portfolio grows itself; you still earn living expenses elsewhere.
- Barista FIRE: portfolio + part-time income together cover everything. No more saving needed.
- Full FIRE: portfolio covers everything; no income required.
People often pass through them in order. Coast first (often in late 30s for diligent savers), then Barista (mid-40s), then Full (50s).
Should you actually stop saving when you hit Coast?
Most people don't, and the math agrees with them. Continuing to save past Coast:
- Brings full FIRE forward by years
- Provides a sequence-risk buffer
- Lets you raise your retirement lifestyle target
- Funds optional things (kids, parents, a bigger house)
Coast FIRE is best treated as a psychological milestone rather than a literal change in behaviour. You've earned the right to stop, even if you don't.
Frequently asked questions
- What real return should I assume for Coast FIRE math?
- 5% is the optimistic standard; 4% is the conservative version that handles bad-sequence risk better. Anything above 6% is wishful thinking.
- Does Coast FIRE work for early retirement, not just 60?
- Yes — you can Coast toward any target age. The compounding window is shorter so the required portfolio is bigger, but the math is identical.
- Can I include my pension contributions in the Coast calculation?
- If you can't stop pension contributions (auto-enrolment), they're part of the unstoppable savings flow. Strict Coast FIRE assumes zero further additions, but it's reasonable to include forced contributions in your base case.
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