Coast FIRE Calculator

What Your Coast Number Means

Coast FIRE is the point where your invested assets, left completely alone, will grow to your retirement target by your chosen retirement age. Once you hit that number, you theoretically only need to earn enough to cover current living expenses with no more retirement saving required. The formula is straightforward: coast number equals your target retirement balance divided by (1 + return rate) raised to the power of years remaining. For example, a 35-year-old targeting $1,000,000 at age 65 with an illustrative 7% average annual return needs approximately $131,000 invested today. If that person already has $180,000, they have cleared the coast threshold by a comfortable margin. Their existing balance would grow to roughly $1,370,000 by age 65 at that illustrative rate, exceeding the $1,000,000 target. The calculator shows your exact coast number, your current surplus or shortfall, and the projected value of your current balance at retirement age.

Assumptions That Change Your Coast Age

The Coast FIRE number is sensitive to three inputs: your target retirement balance, the return rate, and how many years remain until retirement. Small changes in any of them shift the number significantly. Lowering the illustrative return from 7% to 6% raises the 35-year-old's coast number from roughly $131,000 to about $174,000. That single percentage point adds roughly $43,000 to the required balance. Raising the return assumption to 8% drops it to about $99,000. The return rate matters more than any other variable in this calculation. The target balance also has an outsized effect. Deciding you need $1,200,000 instead of $1,000,000 at retirement raises every coast number by 20% across the board. Conversely, a leaner retirement target shrinks the coast number proportionally. Coast FIRE is a planning concept, not a precise commitment. Use the calculator to bracket your coast number under optimistic and conservative assumptions, then revisit annually as your portfolio and plans evolve.

The illustrative return rate you enter is an assumption, not a guarantee. Actual investment returns vary year to year. Revisit your coast number annually.