Coast FIRE is the dollar amount you need invested right now so that compound growth alone, with zero additional contributions, grows into a full retirement fund by a normal retirement age. The formula is your target retirement number divided by (1 plus your assumed annual return) raised to the number of years until retirement. A 30-year-old planning to retire at 65 on $50,000 a year of expenses, using a 7% average annual real return, needs about $117,000 invested today to "coast" the rest of the way, without saving another dollar toward retirement again. You'd still need to earn enough to cover your current living costs, Coast FIRE isn't a way to stop working entirely, it's a way to stop being forced to save.
What Does "Coast FIRE" Actually Mean?
Coast FIRE is a variant of the FIRE (Financial Independence, Retire Early) movement built around a specific milestone: the point where your current investments, left alone, will grow into your full retirement number by the time you want to retire. The name comes from coasting a car down a hill after cutting the engine, once you have enough invested and enough time for compounding to do the work, you can stop shoveling new fuel (savings) into the tank and let momentum carry you the rest of the way. It's different from full FIRE, which means having your entire retirement number invested right now, and different from Barista FIRE, which usually assumes you keep working part-time and still contribute something. Coast FIRE specifically means the investment side of retirement is done. What you do for income between now and retirement is a separate, more flexible question.
How Do You Actually Calculate Your Coast FIRE Number?
Start with your FI number, the total you'd need to retire on using the standard 4% rule: multiply your annual spending by 25. A $50,000-a-year lifestyle needs a $1,250,000 FI number. Then divide that FI number by (1 + your assumed annual real return) raised to the power of years until retirement. Using 7%, the commonly cited long-run inflation-adjusted average for the S&P 500, that's Coast Number = FI Number ÷ (1.07)^years. For a 30-year-old retiring at 65, that's 35 years, so $1,250,000 ÷ (1.07)^35, which works out to roughly $117,000. That's the real answer to "how much do I need to have invested to coast," not a rule of thumb, an actual calculation you can rerun with your own expenses and timeline. For more on where the 4% rule itself comes from and whether it still holds up, our breakdown of whether the 4% rule is still safe in 2026 covers that directly.
Real Examples: What Coast FIRE Looks Like at 25, 30, and 40
The number moves a lot depending on how many years of compounding you have left, which is the entire point of the strategy: start earlier, and you need dramatically less capital to hit the same target.
- Age 25, retiring at 65 (40 years), $40,000/year expenses. FI number: $1,000,000. Coast number at 7% real return: about $66,800.
- Age 30, retiring at 65 (35 years), $50,000/year expenses. FI number: $1,250,000. Coast number at 7% real return: about $117,100.
- Age 40, retiring at 65 (25 years), $60,000/year expenses. FI number: $1,500,000. Coast number at 7% real return: about $276,400.
The gap between the 25-year-old's number and the 40-year-old's number isn't mostly about how much more the older saver spends, it's about how many fewer years of compounding are left to do the work. Fifteen extra years of growth is worth roughly four times the required starting capital in this example, which is the real argument for treating Coast FIRE as a target you build toward as early as possible, not a milestone you check for the first time in your 40s.
What Happens If Your Return Assumption Is Wrong?
Your coast number is only as good as the return assumption behind it, and 7% real is an average, not a guarantee for any specific stretch of decades. Run the same 30-year-old example at a more conservative 5% real return instead of 7%, and the coast number jumps from about $117,100 to about $226,600, nearly double. That's not a small margin of error, it's the difference between a goal that feels close and one that's still a decade of saving away. This is the same underlying risk covered in our piece on sequence of returns risk: the order and size of your actual returns, not just the long-run average, determines what your money is worth when you need it. Treat 7% as an optimistic case, and check your number again with a more conservative assumption before you make any real decisions based on it.
Does Hitting Coast FIRE Mean You Can Stop Working?
No. Coast FIRE means you can stop adding new money to retirement accounts, not that you can stop earning income entirely. You still need to cover your current rent or mortgage, food, insurance, and everything else you spend on between now and retirement age, and for most people that means keeping a job, even if it's a lower-stress, lower-paying, or more flexible one than the career they built while accumulating the coast number in the first place. The freedom Coast FIRE actually buys is optionality on the kind of work you do, not the ability to stop working altogether. Confusing the two is the most common way people miscalculate what hitting this number actually changes about their life.
What Are the Real Risks of Coasting?
- You're locking in an assumption about returns you can't control. As shown above, a lower real return than the historical average meaningfully raises the number you actually needed, and you won't know which scenario you got until decades later.
- Lifestyle inflation quietly moves the goalposts. The FI number is based on your current spending. If your expenses rise faster than inflation over the next 20 or 30 years, kids, a bigger home, more travel, your real coast number was too low from the start.
- You're still exposed to full market risk with no new contributions offsetting a downturn. Once you stop adding money, a bad early stretch has nothing fresh coming in to average down against, which is a real behavioral and mathematical difference from someone still dollar-cost averaging through a decline.
- "Coast" jobs can pay less or disappear. The strategy assumes you can reliably earn enough to cover current expenses without saving more, which isn't guaranteed in every economy, industry, or health situation.
- It's not FDIC- or SIPC-insured growth. The number assumes continued market exposure, typically through index funds or similar investments, which carries real volatility risk the whole way to retirement, not a guaranteed path.
Is Coast FIRE a Genuinely Useful Target, or Just a Reframe?
It's genuinely useful as a checkpoint, not because it changes the math of retirement saving, but because it changes the emotional weight of it. Knowing your specific coast number gives you a concrete, calculable target instead of the vague, moving-goalpost feeling that "save as much as possible for as long as possible" usually produces. Once you can see the actual number for your age and expenses, you can decide deliberately whether to keep saving aggressively past it, or shift that flexibility toward a lower-stress job, a career change, or simply more breathing room in your current budget. The number itself doesn't remove the risk of assuming a return that doesn't show up, but it does turn a fuzzy long-term goal into one you can actually check your progress against with real math.
If you're building toward this kind of number, the mechanics matter as much as the target. Our guide to index funds for people who hate investing covers the simplest way to actually hold the diversified, low-cost investments this math assumes, and our breakdown of how much you should have saved by 30, 40, and 50 gives you a second, independent way to sanity-check your own progress. If you're investing from Canada, Wealthsimple is a straightforward, low-fee platform for holding exactly this kind of long-term index position; see our full resources list for more.
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Spicy Investing