Most people think of retirement savings as a lifelong obligation - contribute every year until you finally stop working. Coast FIRE flips that assumption. The idea is simple: save aggressively early in your career, reach a specific target, and then stop making additional retirement contributions entirely. From that point, compound interest does the heavy lifting, growing your existing balance to a full retirement number by the time you actually want to retire.
Coast FIRE is a milestone, not a destination. You hit Coast FIRE when your current invested assets are large enough that, even if you never contributed another dollar, they would grow to your full FIRE number by your target retirement age. Once you reach it, you no longer need to save for retirement - you just need to cover your living expenses with your income, which is a much easier bar to clear.
The name comes from the image of a boat cutting its engine and coasting to shore. You did the hard work of getting up to speed; now you let momentum carry you in.
The Coast FIRE number is derived from the future value formula run in reverse. If you know how much you need at retirement (your FIRE number), you can discount it back to today using your expected real rate of return and the number of years until retirement:
For example, suppose your FIRE number is $2,000,000 and you plan to retire at 65. If you assume a 6% real annual return and you are currently 35, that is 30 years of growth. Your Coast FIRE number would be roughly $2,000,000 / (1.06)^30 = approximately $348,000. Reach $348,000 by age 35 and you can, in theory, stop all retirement contributions and still hit $2M by 65.
Imagine someone who graduates college at 22, keeps expenses low, and saves $25,000 per year into index funds. Assuming a 7% nominal return, they might reach $350,000 by age 35 - roughly 13 years of disciplined saving. At that point, they shift gears. They take a lower-paying job they actually enjoy, stop contributing to retirement accounts, and simply cover their day-to-day expenses. Their portfolio, left alone, compounds from $350,000 to well over $2,000,000 by age 65, even without a single additional dollar invested.
Those middle decades - ages 35 to 65 - can look very different from a traditional career grind. Lower income, more flexibility, more time. The Coast FIRE number is what makes that possible.
Standard FIRE means accumulating enough assets to cover all expenses indefinitely through passive investment income - typically 25 times annual spending (the 4% rule). At that point you can stop working entirely. Coast FIRE does not get you there immediately. You still need a job or some income source to pay for food, rent, and everything else. The difference is that you are freed from the pressure of saving for the future - your future is already funded. You only need to break even today.
For many people, the mental burden of retirement saving is more stressful than the work itself. Coast FIRE offers a middle path: you do not have to grind at a high-income job for 20 more years, but you also do not have to fully retire tomorrow. Part-time work, freelancing, passion projects, and lower-cost living all become viable because you only need to cover current expenses, not also stockpile for 30 years of retirement.
You still need reliable income throughout the coasting years. If your income disappears and you have to draw down the portfolio before retirement age, the compound growth math breaks down. Coast FIRE is most durable when paired with at least some income - even part-time - that covers living expenses without touching investments.
This calculator computes your Coast FIRE number automatically alongside your full FIRE number. Enter your current savings, expected return, target retirement age, and annual spending. The tool shows you how much you need today to coast, how long it will take to reach that number at your current savings rate, and how your portfolio projects forward under both coasting and continued-contribution scenarios. You can use the comparison to decide when - and whether - coasting makes sense for your situation.
I feel like Coast FIRE is almost kind of a safety net more than anything else. Especially now with AI possibly taking everyone's jobs in tech, it genuinely gives me comfort knowing that I could survive off of something like a barista job with health insurance if I had to. The number is already working for you, you just have to not panic and let it