What if the smartest move for your retirement account this year is to stop putting money into it?
That question sounds like heresy in a personal-finance world built almost entirely around the instruction to save more, contribute more, and never let up. A specific, calculable point exists where the math flips: the moment your invested retirement balance is large enough that compound growth alone, with zero additional contributions, will carry you to your target number by the age you want it. Personal-finance writers in the FIRE community — financial independence, retire early — gave this scenario a name years ago: Coast FIRE. You've hit your coast number when you could stop contributing entirely, leave your investments parked and growing, cover your current cost of living out of your paycheck alone, and still arrive at a full retirement account on schedule.
What Coast FIRE Actually Means
Coast FIRE is not early retirement, and that distinction trips people up constantly: you are still working, still earning a paycheck, and still paying your own rent or mortgage out of current income. What changes is the pressure on your retirement contributions specifically, and only that. Once you've reached your coast number, every dollar you were previously funneling into a 401(k) or IRA becomes optional rather than mandatory — money you can redirect toward a house down payment, a career change into lower-paying but more satisfying work, extended time off, or simply a less stressful monthly budget. The retirement piece of your financial life is, in effect, done. It just needs three or four decades to finish compounding, quietly, in the background, while you spend the rest of your income on whatever you actually want it to do.
Younger readers tend to hear this and assume it means quitting a job. It doesn't. A barista, a teacher, a freelance graphic designer, and a corporate VP can all be equally "coasted" on their retirement number while doing completely different work at completely different income levels — the only thing Coast FIRE measures is whether your existing balance, left alone, gets you there.
The Math Behind a "Coast Number"
The calculation rests on one assumption: the long-run historical average return of the stock market, adjusted for inflation, runs at roughly 7% a year. That figure comes from many decades of market data, spanning multiple recessions, wars, and stretches of double-digit inflation, and it's the number financial planners typically lean on for long-horizon compounding estimates. It isn't a promise about next year, or even next decade — some ten-year stretches beat it by a wide margin, and some fall well short. At a 7% annual return, money roughly doubles every ten years, a rough version of the "Rule of 72": divide 72 by your expected annual return, and you get the approximate number of years it takes a balance to double. Run that math forward over three or four decades and the doubling compounds on itself, which is the entire mechanism behind Coast FIRE. Get a large enough sum invested early, structure it so you're not touching it, and the doubling does the heavy lifting without another contribution ever landing in the account.
Run the numbers on a couple of realistic starting points. A 35-year-old with $120,000 already invested in retirement accounts, left untouched and growing at that same 7% real return, would reach roughly $913,000 by 65 — no further contributions required, just time and the market doing what markets have historically done. Push the start earlier and the number required drops sharply: a 27-year-old with $50,000 invested reaches close to $654,000 by 65 on the same assumption, because eleven extra years of compounding does a disproportionate amount of the work. That's the actual argument for saving aggressively in your twenties rather than your forties — not virtue, just exponents.
How to Ballpark Your Own Coast Number
The formula is one line of math, and you don't need a financial planner to run it. First, estimate your full retirement number the same way the 4% rule does: roughly 25 times your expected annual spending in retirement. Second, decide how many years stand between now and the age you want to stop actively saving. Third, divide your retirement number by 1.07 raised to the power of those remaining years — that division undoes the compounding and tells you what balance you'd need sitting in your accounts today for growth alone to finish the job. A 45-year-old aiming for a $1,000,000 retirement number by 65 needs roughly $258,000 invested right now to coast the rest of the way. Someone targeting $1,500,000 by 60, fifteen years out, needs closer to $544,000 today. Neither of those numbers is small, which is exactly the point: Coast FIRE rewards early, aggressive saving far more than it rewards catching up later. Log into your own 401(k) and IRA providers, add up the actual balances, and run this same division with your real target and your real timeline, because a napkin estimate from a stranger's example is not a substitute for your own numbers.
Coast FIRE vs. Lean FIRE, Fat FIRE, and Barista FIRE
None of these terms are interchangeable, and conflating them is the fastest way to build a plan around the wrong number.
Traditional FIRE means you've saved enough, in total, to cover your full living expenses by withdrawing from your portfolio indefinitely — usually calculated using a 4% initial withdrawal rate, which lets you quit working altogether. Lean FIRE runs that same idea on a stripped-down budget, often under $40,000 a year in expenses, which lowers the total number needed but also caps the lifestyle it buys, permanently. Fat FIRE goes the other direction: a larger number that supports a more comfortable, less constrained retirement, frequently built around $100,000 or more in annual spending. Barista FIRE sits closer to Coast FIRE conceptually — you've saved enough that a part-time job, often one that carries employer health insurance, covers your current expenses while your retirement accounts keep growing untouched in the background. Coast FIRE is narrower than all of them: it says nothing about when you stop working full-time, only that your retirement number is already locked in.
Where the Math Gets Fragile
The 7% assumption holds up well across long stretches of market history, but it says nothing about the specific ten-year window that happens to follow your last contribution. A downturn that lands in your first five years of coasting — rather than getting smoothed out over three decades — can knock a real dent into a balance that has no new money coming in to average down against. This is called sequence-of-returns risk, and it's the honest caveat most Coast FIRE explainers skip past. Inflation is the other variable worth sitting with: the 7% figure already accounts for it, but if actual inflation runs hotter than the long-run average for a sustained stretch, your coast number effectively moves further away even while your account balance keeps climbing in nominal terms.
There's a second, more mundane problem: stopping contributions entirely usually means walking away from an employer 401(k) match, and that's a bad trade. Don't do it. Most employers that offer a match require an active contribution from you to unlock it — free money that disappears the moment your own contribution drops to zero. The better version of Coast FIRE, and the one actually worth recommending, is contributing just enough to capture the full match and letting the rest of your paycheck go toward other goals, rather than cutting retirement savings off completely.
The Piece Most Coast FIRE Calculators Skip: Health Insurance
If you're using Coast FIRE to justify stepping down to part-time work or freelance income in the U.S. before 65, run your health insurance numbers before you run your retirement numbers. Medicare eligibility doesn't start until 65, which means anyone coasting through their thirties, forties, or fifties needs either an employer plan, a spouse's plan, or an individual policy through the ACA marketplace at healthcare.gov — and premiums on that exchange vary enormously by state, age, and household income, in ways a retirement calculator never touches. Barista FIRE quietly wins the argument over pure Coast FIRE for a lot of people on exactly this point: a part-time job that comes with group health coverage can be worth more than the extra hours of income it replaces.
Who Coast FIRE Actually Fits
Picture the specific situation where this makes sense: you're 32, you front-loaded retirement contributions in your twenties while your expenses were low and your risk tolerance was high, and you're now sitting on $150,000 or more across a 401(k) and a Roth IRA. You're tired of treating every raise as more money to shovel into index funds, and you'd rather have breathing room to switch industries, work fewer hours, or take a pay cut for a job you actually want. That's a real, defensible use of Coast FIRE — you're not gambling with your future, you're redirecting money that's no longer doing urgent work. It's a much shakier plan if you're 24 with $15,000 invested, hoping thirty-odd years of compounding will quietly cover a gap you haven't actually calculated; run your own numbers against your real balance and a conservative return assumption before you trust a spreadsheet somebody else built.
Coast FIRE isn't a shortcut and it isn't a hack. It's a math problem with your specific numbers plugged in, and the answer is either yes, you've cleared the bar, or no, you haven't yet. Do the arithmetic with your real account balances before you change a single contribution.