The Direct Answer
FIRE stands for Financial Independence, Retire Early. Most FIRE flavors are about retiring as soon as possible, which demands an enormous pile of money. Coast FIRE is the relaxed cousin: you reach the point where the money you have already invested will grow into a full retirement fund on its own, with no further contributions. From that day forward, your only financial job is paying your current bills. You keep working, but none of your paycheck has to go toward retirement anymore. The heavy lifting is over; compound interest takes it from here.
Think of it like pushing a car up a hill. Full FIRE is pushing it all the way to the summit. Coast FIRE is pushing it just far enough that it rolls over the crest on its own momentum. You still have to steer, keep gas in it, and not let it roll off a cliff, but the pushing part is done. That is why so many people who have been investing steadily for a decade discover they are already coast FIRE without ever having planned for it.
The Coast FIRE Formula
Your coast number comes from two standard planning tools: the 4% rule and compound growth. First, figure your retirement target. The 4% rule says you can withdraw about 4% of your investments per year in retirement without running out, so your target is 25 times your annual spending. Spend $50,000 a year in retirement, and you need $1,250,000 on retirement day.
Second, ask: how much money today grows into that target by the time you retire? That is the present value of your target, discounted by the growth rate:
Coast FIRE number = retirement target / (1 + r)^t
Here r is your assumed real annual return, the part of market growth left over after inflation, and t is the number of years until you retire. The standard planning assumption is 7% real (roughly 10% nominal stock returns minus 3% inflation). This is the same math running under the hood of our compound interest calculator, so the numbers below match what you will see there.
Worked example. You are 30, you plan to retire at 60, you expect to spend $50,000 a year in retirement, and you assume 7% real growth. Retirement target: 25 x $50,000 = $1,250,000. Years of growth: 30. Divide: $1,250,000 / (1.07)^30 = $164,200 (about $150,000 if you count the small boost from monthly compounding, which the calculator applies by default). So if you have roughly $150,000 to $165,000 invested at age 30, you can stop saving for retirement entirely, and compounding alone carries that balance to around $1.22 million by age 60, enough to support about $48,700 a year at a 4% withdrawal rate. You never add another dollar.
Your Coast Number by Age
This table shows the coast number for a retirement at 65 with $50,000 in annual spending ($1,250,000 target), using the 7% real assumption with monthly compounding, exactly as the calculator computes it:
| Your age today | Years to 65 | Coast number |
|---|---|---|
| 25 | 40 | $77,000 |
| 30 | 35 | $109,000 |
| 35 | 30 | $154,000 |
| 40 | 25 | $218,000 |
| 45 | 20 | $310,000 |
| 50 | 15 | $439,000 |
| 55 | 10 | $622,000 |
| 60 | 5 | $882,000 |
Two patterns matter. First, time does the heaviest lifting: a 25-year-old needs less than half what a 35-year-old needs for the same retirement, because each dollar gets forty years of compounding. Second, the coast number rises sharply as the years shrink, which is the same lesson behind our compound interest explainer: growth is back-loaded, and the last decade does a disproportionate share of the work.
If your spending differs from $50,000, scale the numbers proportionally. Coast number is linear in spending: spend $80,000 a year, and every row is 1.6x larger (the 30-year-old then needs about $174,000).
Coast FIRE vs Lean FIRE vs Fat FIRE vs Barista FIRE
Coast FIRE often gets confused with its siblings, but they describe genuinely different situations. Coast FIRE means your investments already cover your future retirement, so you stop contributing and keep working. You do not quit; you just stop pushing.
Lean FIRE is full retirement on a bare-bones budget. You quit working entirely, living on 4% of a modest pile. If you can live on $30,000 a year, lean FIRE needs 25 x $30,000 = $750,000 saved, and that is the whole pot, no coasting from here.
Fat FIRE is the mirror image: full retirement on a high-spending lifestyle. Want $150,000 a year in retirement? That is 25 x $150,000 = $3,750,000. Fat FIRE is the most money-demanding flavor of all.
Barista FIRE sits between lean and coast. You quit the career job but work part-time, enough to cover current expenses and usually to keep health insurance, while your investments coast. The part-time work is the safety valve: it stretches the runway and protects the invested money from being touched early.
Here is the practical hierarchy of difficulty. Coast FIRE is the easiest and the most common, because you need far less money than the others and you keep earning. Lean and barista FIRE demand you give up the salary. Fat FIRE demands you give up almost nothing, which is why almost nobody reaches it.
When Coast FIRE Works
It works when you are genuinely done saving and the math has slack in it. Run the stress test: recompute your coast number at 5% real growth instead of 7%. If the number you already have invested still clears the bar, your coast is sturdy. It works when your spending estimate is honest, based on your actual budget rather than a fantasy of a cheaper future. And it works best when the investments are ones you will actually leave alone: retirement accounts you are not borrowing from, brokerage accounts you do not raid for vacations.
Coast FIRE also works psychologically in a way the extreme flavors often do not. Quitting work at 40 sounds heroic until you do it. Dropping retirement savings to zero and taking the job you actually enjoy, the lower-stress role, or the four-day week is a life change most people can sustain. The financial freedom is partial, but it is real: every dollar you earn now is for the present, not the future.
When It Does Not Work
It does not work on inflated return assumptions. If you plan on 10% or 12% real returns, you are not coasting, you are gambling. The 7% figure is already generous; history says it is the long-run average, not a promise. Run the 5% stress test and take the result seriously.
It does not work if your future spending is a guess. The coast number is linear in spending, so a 20% underestimate of your retirement lifestyle means a 20% hole in the plan. Costs people forget: health insurance before Medicare, property taxes, cars, home repairs, and helping kids or parents. If you have a mortgage, its payment must be part of the spending estimate until it is gone, so check the real numbers in our mortgage payment guide before declaring victory.
And it does not survive being raided. The entire model assumes the money compounds untouched for decades. Pull $30,000 out at 40 for a renovation and you have not just lost $30,000, you have lost what $30,000 would have become, roughly $163,000 by 65 at 7% monthly compounding. Every early withdrawal costs about five times its face value. Coast means the money stays invested.
How to Check If You Are Already Coasting
Open our compound interest calculator and set the monthly contribution to zero. Enter your current invested balance, a 7% rate, and the number of years until you retire. Multiply your expected annual retirement spending by 25. If the projected balance meets or beats that target, you are coast FIRE: your savings will get you there without another contribution. If it falls short, the gap is how much more you need, and raising the rate to test 5% shows how much margin you have.
A surprising number of people in their 30s with a decade of steady 401(k) contributions discover they crossed the line a while ago. If that is you, the honest next question is not whether to celebrate but what to do with the freed-up savings: build the emergency fund, attack debt, or simply spend more of the present. Coasting is the prize, but you still have to use it well.
Frequently Asked Questions
How much do I need to coast FIRE?
Divide your retirement target (25 times your annual spending, per the 4% rule) by the compound growth factor for the years until retirement. At 7% real annual growth retiring at 65, a 30-year-old spending $50k a year needs about $109,000 invested today; a 40-year-old needs about $218,000. Plug your numbers into our free compound interest calculator with $0 monthly contributions to find your exact figure.
What is the coast FIRE formula?
Coast FIRE number = retirement target / (1 + r)^t, where the retirement target is 25 times your annual spending, r is your assumed real annual return (7% is the common planning figure), and t is the number of years until you retire.
What is the difference between coast FIRE, lean FIRE, and barista FIRE?
Coast FIRE means your investments already cover retirement on their own, so you stop saving and just cover current bills. Lean FIRE means retiring fully on a bare-bones budget, with 25 times a minimal annual spend invested. Barista FIRE is lean FIRE plus part-time work to cover expenses and often health insurance. Fat FIRE is the opposite of lean: retiring with 25 times a high-spending lifestyle saved up.
Is coast FIRE realistic for most people?
It is the most reachable form of FIRE, because it requires far less than a full retirement number. Anyone who invested steadily in their 20s and 30s may already be coasting without knowing it. The main risks are overestimating future returns, underestimating future spending, and the temptation to raid the invested money early.
Can I coast FIRE with a mortgage or debt?
High-interest debt makes coast FIRE shaky, because the money tied up in interest payments should be earning 7% instead. A mortgage is less of a problem if it will be paid off by retirement, but its payment must be part of your projected retirement spending. Run the numbers on your loan in our mortgage payment guide before counting yourself as coasting.
What return should I assume for coast FIRE math?
7% real annual return is the standard planning assumption, meaning roughly 10% nominal stock-market returns minus 3% inflation. Using 5% instead is the conservative stress test: if your coast number still works at 5%, it is genuinely safe. Avoid planning on 10% or higher.
Keep Reading: Finance Guides
The coast model is built on compounding, so if the math above felt shaky, start with how compound interest works, the formula, the Rule of 72, and why starting early beats saving more. To size your spending side honestly, work through how to calculate mortgage payments and how to calculate percentages, and for the everyday side of the budget, how to calculate a tip keeps small numbers from drifting.