What is Coast FIRE?

Traditional FIRE (“Financial Independence, Retire Early”) means saving enough to stop working entirely. Coast FIRE is a softer milestone: the day your portfolio is big enough that if you never contribute another dollar, compound growth alone will carry you to a full retirement by your target age.

You still work. You just don’t have to save for retirement anymore.

For most people, Coast FIRE arrives ten or fifteen years before traditional FIRE, and the lifestyle shift it unlocks — cut hours, switch to a lower-paid job you care about, take a sabbatical — often matters more than the formal retirement date.

The math in one formula

Coast FIRE asks: how much do I need today so that it grows into my retirement number by the time I retire?

If:

• T = target retirement portfolio (your full FIRE number)
• r = expected real (inflation-adjusted) return
• n = years until retirement

Then the Coast FIRE number is:

Coast FIRE = T / (1 + r)ⁿ

Plug in numbers: say you want $1,250,000 in today’s dollars to retire at 65 (a 4% safe withdrawal rate covering $50k/year of spending), you’re 35 today, you assume 5% real returns, and you’ve got 30 years.

$1,250,000 / (1.05)³⁰ ≈ $289,000

If you can get to $289,000 invested by age 35 and never add another dollar, compound growth gets you to $1.25M by 65. That’s Coast FIRE.

Why the number is smaller than people expect

Compound growth is front-loaded. The first dollar you invest gets 30 years of compounding; the dollar you invest at 64 gets one year. That’s why the Coast FIRE number for a 30-year-old can be a quarter of the final target, while for a 55-year-old it’s nearly the full target.

A quick reference at 5% real returns and a $1.25M target at 65:

Age today	Years to 65	Coast FIRE number
25	40	$177,000
30	35	$227,000
35	30	$289,000
40	25	$369,000
45	20	$471,000
50	15	$601,000
55	10	$767,000
60	5	$979,000

Hitting Coast FIRE in your 30s is a dramatically different exercise than hitting it in your 50s. This is why “contribute aggressively early” is the single most actionable FIRE advice — the Coast FIRE number gets much harder to reach the longer you wait.

Coast FIRE vs. Barista FIRE vs. Full FIRE

The FIRE community has a few adjacent concepts:

• Full FIRE: portfolio can cover 100% of your spending indefinitely. You can stop working entirely. Usually the largest number.
• Coast FIRE: portfolio can grow into Full FIRE by retirement age without more contributions. You still work to cover current living expenses, but not for retirement.
• Barista FIRE: portfolio covers most retirement spending, but you work part-time or in a low-stress job (often for healthcare benefits — hence “barista”) to fill the gap. Usually lands between Coast and Full FIRE.
• Lean FIRE / Fat FIRE: same math, different lifestyle assumptions. Lean assumes minimal spending; Fat assumes upper-middle-class comfort.

These are reference points, not rules. Most people move through them in order.

What Coast FIRE actually buys you

Reaching Coast FIRE doesn’t mean quitting your job. It means the reason you work changes. Before Coast FIRE, every paycheck has two jobs: pay the bills today, and fund retirement. After Coast FIRE, a paycheck only has to cover current spending.

That unlocks real choices:

• Downshift to a job you actually like, even if it pays 30% less.
• Cut hours. Four days a week, three days, part-time — the math still works.
• Take unpaid sabbaticals or career breaks without derailing retirement.
• Launch a business or switch careers without worrying that zero income years nuke your long-term plan.
• Stay in a high-cost-of-living area you love, because you don’t need to maximize savings.

A lot of Coast FIRE adherents never formally “retire” early — they just gradually reshape their working life around what matters. That’s not a compromise. That’s kind of the point.

The assumptions that can wreck it

Coast FIRE math is extremely sensitive to the assumed real return. A 1 percentage point lower return compounds into a much bigger required number.

Same $1.25M target at 65, age 35 today:

Real return assumption	Coast FIRE number
7%	$164,000
6%	$218,000
5%	$289,000
4%	$384,000
3%	$515,000

The broad US stock market has delivered ~7% real historically, but conservative retirement planning often uses 5% to account for international diversification, bonds, and sequence-of-returns risk.

Other common blind spots:

• Healthcare. If you’re counting on retiring at 65, you’ll be on Medicare. If you’re coasting earlier, your spouse’s job-based insurance or ACA subsidies fill the gap — but that gap is expensive and politically unstable.
• Inflation. The formula above uses real returns, so inflation is already factored in. Don’t double-count.
• Market timing. If you hit Coast FIRE right before a 50% bear market, you might slip back below the line. Some coasters keep contributing for a year or two past the technical number for safety.

How to know when you’ve hit it

The simplest test:

1. Pick a target annual spending in retirement (today’s dollars).
2. Multiply by 25 to get the target portfolio (the 4% rule).
3. Divide by (1 + real_return)years_to_retirement.
4. Compare to your current invested portfolio (exclude primary home equity, include 401(k)/IRA/brokerage).

If your portfolio ≥ the Coast number and you’re comfortable with your return assumption, you’re at Coast FIRE. Our retirement calculator handles the calculation interactively — including sensitivity to return, inflation, and target spending.

Further reading

• Retirement / FIRE calculator — project your full FIRE and coast numbers together
• The 4% rule — where the 25x multiplier comes from
• Compound Interest calculator — play with return assumptions interactively
• FIRE movement explained — the broader framework and its critics