Coast FIRE Number Calculator
Your Coast FIRE number is the single figure that tells you whether you can stop saving. Enter your details to calculate it instantly.
Coast FIRE Calculator
Discover if your current savings are enough to grow to your retirement goal without additional contributions. Get instant, accurate calculations with no signup required.
What your Coast FIRE number means
If your invested assets are at or above your Coast FIRE number, you've reached the milestone - compound growth can take over from here. If you're below it, the gap tells you how much further to go.
Because the number depends on how many years of compounding remain, it grows as you age. Time in the market is the biggest lever you have.
How your Coast FIRE number is calculated
Your Coast FIRE number answers a single question: how much do you need invested today so that compound growth alone reaches your retirement goal? The formula works in two steps. Start with your full FIRE number - annual retirement spending divided by your safe withdrawal rate (a 4% rate turns $40,000 of spending into a $1,000,000 target). Then discount that target back to the present: divide it by (1 + your expected return) raised to the number of years until you retire.
Example: at 35, retiring at 65, needing $50,000 a year, your FIRE number is $1,250,000. With a 5% real return over 30 years, 1.05^30 is about 4.32, so your Coast FIRE number is roughly $289,000. Have that invested today and you can stop contributing - the balance is projected to grow into your full target by 65.
What makes your number go up or down
Three inputs move your Coast FIRE number the most. Time is the biggest lever: every extra year until retirement gives compounding more room, lowering the amount you need today. A higher expected return lowers it too, while a more conservative return raises it. And your spending target scales the whole thing - trimming future expenses, or counting on guaranteed income, shrinks the number directly.
This is why the same person can have very different Coast FIRE numbers depending on assumptions. It is worth calculating a range rather than a single figure: a best case with optimistic inputs and a cautious case with conservative ones gives you a band to aim for instead of a false sense of precision.
Coast FIRE number vs your full FIRE number
These two numbers are easy to confuse. Your full FIRE number is what you ultimately need to live off your portfolio - usually around 25 times your annual spending. Your Coast FIRE number is much smaller: it is only the amount you need today so that, with no further contributions, growth fills the gap to that full number by retirement. The further you are from retirement, the larger the gap compounding can close, and the smaller your Coast FIRE number is relative to your FIRE number.
Reaching your Coast FIRE number is therefore a milestone, not the destination. You still need to cover your living costs until retirement, and your portfolio still has to actually deliver the returns you assumed. But it marks the point where saving for retirement becomes optional.
What to do if you are below your number
If your invested assets are under your Coast FIRE number, the gap tells you exactly how much further you have to go - and you have several levers. Increasing contributions is the obvious one, but extending your retirement age, lowering your future spending target, or reducing investment fees can each move you toward the milestone without saving an extra dollar. Because compounding rewards time, contributions made earlier count for far more than the same amount saved later.