Coast FIRE calculator

How to calculate your Coast FIRE number

Your Coast FIRE number is the amount invested today that could grow to your retirement target without additional contributions, if the assumptions hold.

Reviewed by ZW Studio, maker of Coastful · Updated August 12, 2026

Step 1: estimate the retirement target

A common starting point divides expected annual retirement spending by a chosen withdrawal rate. This is a planning assumption, not a guarantee.

If expected annual spending is $60,000 and the chosen rate is 4%, the simple target is $1.5 million. Taxes, benefits, pensions, changing spending, and investment fees can all change what is appropriate.

Step 2: discount the target to today

Use an expected real return—growth after inflation—so the result stays in today's purchasing power.

For a $1.5 million target, 25 years to retirement, and a 5% real return, the illustrative Coast FIRE number is about $443,000. In other words, $443,000 growing at that assumed rate for 25 years would reach roughly $1.5 million without new contributions.

Step 3: test the assumptions

A single answer can look more certain than it is. Recalculate with lower returns, higher spending, a later or earlier retirement age, and a more conservative withdrawal rate. The SEC's Investor.gov compound interest calculator is another useful way to examine how time and return assumptions affect growth.

• Spending: use an annual amount that includes irregular expenses.
• Inflation: keep spending and return assumptions in either real or nominal terms consistently.
• Current portfolio: include investable assets intended for retirement, not every asset you own.
• Scenario range: compare an optimistic case with a conservative case.

How Coastful makes the estimate more personal

Coastful runs FIRE projections from the assets, liabilities, expenses, allocation, inflation, and withdrawal rate you enter. Its what-if scenarios let you change one assumption without rebuilding the plan. Data and calculations stay on your device, except for an optional anonymous exchange-rate request when multi-currency mode is used.