Coast FIRE: When You Can Stop Saving for Retirement

Most retirement advice assumes you'll save steadily for forty years. But there's a milestone, often reached far earlier, that changes the maths entirely: the moment your existing investments are enough to grow into your full retirement number on their own, without another dollar of contributions. That's Coast FIRE — and reaching it can quietly transform your relationship with work.

What Coast FIRE actually means

FIRE — financial independence, retire early — means having enough invested to live off forever. Coast FIRE is a waypoint on the road there. You've reached it when your current investments, left completely alone, will compound into your FIRE number by the time you retire. You still need a job to cover today's living costs, but you no longer need to save for retirement. The retirement part is handled; you're just coasting.

The two numbers behind it

Your FIRE number is what you need invested to retire: annual spending divided by a safe withdrawal rate. At the common 4% rate, that's 25× your yearly spending. Spend $40,000 a year, and your FIRE number is $1,000,000.

Your coast number is that target discounted back to today. It's how much you'd need invested right now for growth alone to reach the FIRE number by retirement:

Coast number = FIRE number / (1 + r)^years to retirement

Here r is your expected real (after-inflation) return — using a real return keeps everything in today's money. When your current savings reach the coast number, you've reached Coast FIRE.

Worked example

You're 30, plan to retire at 60, spend $40,000 a year, and expect a 5% real return:

• FIRE number: $40,000 ÷ 0.04 = $1,000,000
• Coast number today: $1,000,000 ÷ (1.05)³⁰ ≈ $231,000

If you already have $231,000 invested, you've coasted. Touch nothing, add nothing, and at 5% real growth it becomes roughly $1,000,000 by 60. From here, you only need to earn enough to pay your bills — retirement saving is optional.

Why it's so powerful early

The coast number falls dramatically the more years you have. The same $1,000,000 target needs only ~$231,000 at age 30, but ~$377,000 at age 40 and ~$614,000 at age 50 — because there's less time for compounding to work. Front-loading your saving in your twenties and early thirties is worth far more than the same effort later. Hit Coast FIRE young and you buy yourself decades of optionality.

What it frees you to do

Coast FIRE isn't about quitting — it's about choice. Once retirement is funded, the pressure comes off the savings rate, which can let you:

• Take a more meaningful but lower-paying job without derailing retirement.
• Go part-time, freelance, or take a career break.
• Redirect what you were saving toward nearer-term goals — a house, travel, or simply more breathing room.
• Stop worrying about retirement entirely and focus on covering present expenses.

The cautions

• Real returns aren't guaranteed. The maths assumes a steady real return; markets don't deliver that smoothly. A long weak stretch can leave you short, so keep a margin of safety and re-check every few years.
• Lifestyle creep raises the target. If your spending rises, your FIRE number rises with it, and you may slip back below the coast line. Coast FIRE assumes your future spending matches today's estimate.
• You still need income. This is the big one — Coast FIRE is not early retirement. You must cover your living costs until you actually retire.

Coast FIRE vs other FIRE flavours

Full FIRE means your investments cover your living costs now. Lean FIRE and Fat FIRE describe the size of the target (frugal vs. generous spending). Coast FIRE is unique in that it's about timing — the point where you can stop contributing, even if full independence is still years away.

To project the balance itself over time, use the retirement calculator, and read the FIRE movement explained for the bigger picture and where the 4% rule comes from.