Coast FIRE Explained: When You Can Stop Saving and Let Compound Interest Finish the Job

Of the FIRE variants we touched on in our FIRE overview, Coast FIRE is the one that seems to surprise people the most — mostly because it doesn't actually require you to stop working. It just changes what your paycheck needs to cover.

What "coasting" actually means

Once you've saved enough that compound growth alone will carry that balance to your full retirement number by your planned retirement age, you no longer need to add another dollar to retirement accounts. Your existing money is already on track to finish the job on its own. From that point forward, whatever you earn only needs to cover your current living expenses — not retirement savings on top of them.

This is different from Lean, Fat, or full FIRE, which are all about the number you need to actually stop working. Coast FIRE is about the number that lets you stop saving, well before you stop working.

How to estimate your own Coast FIRE number

The math is just compound interest run in reverse. Instead of asking "what will this balance grow to," you ask "what balance today grows to my target by then":

Coast number = Retirement target ÷ (1 + return)^{years until retirement}

Say your full retirement target is $1,250,000, you're 30 years from your planned retirement age, and you're assuming a 7% annual return. Divide $1,250,000 by 1.07 raised to the 30th power, and you get a Coast FIRE number of roughly $164,000. Once your balance hits that, in theory, you could stop contributing entirely and still arrive at $1,250,000 by the same retirement age, purely from growth.

One thing worth double-checking here: your target and your return rate need to speak the same "dollar language." If your $1,250,000 target is in today's dollars, use a return that's already net of inflation (a real return) to match it. If it's already inflated forward to what it'll actually cost in future dollars — the way our calculator's goal step handles it — use your full nominal return instead. Mixing the two (today's-dollar target with a nominal return, or vice versa) throws the math off and can make your Coast number look smaller, or bigger, than it really is.

Years until retirement	Coast number needed (target: $1,250,000, 7% return)
20 years	~$323,000
25 years	~$230,000
30 years	~$164,000
35 years	~$117,000

The more years you have left, the lower your Coast number — which is exactly why this tends to show up as an option for people in their late 20s and 30s who saved aggressively early on, rather than something most people reach right before a traditional retirement age.

Check your own Coast number with the calculator

You can approximate this using our retirement calculator directly: enter your current savings, set Monthly Contribution and Employer Match to $0, and see what the projected balance comes out to at your retirement age. If that projected number already meets or beats your target, you've effectively reached Coast FIRE at your current balance and return assumption.

What it doesn't mean

Reaching Coast FIRE isn't the same as being done. You still need income to cover today's living expenses — rent, food, everything else — for however many years remain until retirement. It also assumes your projected return holds up over that whole stretch, which real markets don't guarantee year to year. Think of it less as a finish line and more as a shift: the pressure comes off retirement savings specifically, which for a lot of people is enough to justify a lower-stress job, fewer hours, or a career change they'd been putting off.

This article is for educational purposes only and is not financial advice. The example above uses a fixed hypothetical return for illustration; actual investment returns vary and are not guaranteed.