How to Calculate Your Coast FIRE Age
By Retire Growth · Updated 2026-10-27 · No independent professional financial review is claimed.
Why the age you reach Coast FIRE differs from the age you plan to retire.
Your Coast FIRE age is the point when your invested savings first meet the balance needed to grow toward your later retirement target without further deposits. Your retirement age is when that portfolio would need to begin covering retirement spending. They are different dates, and the gap between them is the coast period.
The threshold moves as time passes
A future target has a smaller present value when there is more time for positive real growth. As retirement approaches, the Coast threshold rises toward the full target. A fixed “Coast number” calculated at age 30 is not the threshold at age 40.
The calculator compares the investment balance with the threshold at each month, rather than checking against today's threshold forever. This matters when saving takes many years.
Ongoing deposits change the crossing date
Current investments grow at the chosen real rate. Monthly savings are added at month end. We ask when that combination first equals the discounted target for the time still remaining.
The tool holds monthly deposits constant in today's purchasing power. If prices rise, the nominal contribution would need to rise to keep that assumption true. A fixed nominal payroll amount is a different scenario and may produce a later crossing.
An example with two dates
In the default illustration, a person is 32, has $80,000 invested, saves $1,500 per month in today's dollars and aims for retirement at 65. A $4,000 monthly budget and a 4% target-sizing withdrawal rate imply a $1,200,000 portfolio target. A 7% nominal return and 3% inflation imply about 3.8835% real annual growth.
The calculator finds the first crossing at age 53 years and 3 months. That is the modeled savings milestone. Age 65 remains the point when the retirement target is needed. Dollar balances and the monthly recurrence can be checked in the methodology.
If there is no crossing
A result of “not reached” means the entered savings pace does not meet the threshold by the target retirement age. It does not mean financial independence is impossible. It means the selected combination of inputs does not produce a crossing in this model.
The additional-savings figure solves for the difference between your current monthly amount and the constant real monthly saving that would reach the full target at retirement. It does not check affordability or tell you which input to change.
Ages beyond the model
No calculation of a future age can promise health, continued work, market returns or a particular lifespan. Long horizons amplify uncertainty. A target above age 90 is allowed with a caution so you can explore the arithmetic without interpreting an unusually long horizon as an endorsed plan.
See what Coast FIRE means for the distinction between working income and portfolio income. The withdrawal-rate guide explains why the target itself is an assumption.
Updated October 27, 2026. Educational content; no independent professional financial review is claimed.