What the Coast FIRE number means
The calculator first divides annual retirement spending by the selected withdrawal rate to form a retirement portfolio target in today’s dollars. It then discounts that future target back over the years between the current and retirement ages using the entered annual real return. The result is the invested balance that would need to be present today under those assumptions.
Coasting assumes no additional contributions
Coast FIRE does not mean retirement today. It describes a scenario in which the current invested balance is left to compound until the selected retirement age without new contributions or withdrawals. Employment income would still need to cover current living costs and any goals outside this model.
Use a real return with a real target
Spending is entered in today’s purchasing power, so growth must also be expressed after inflation. A nominal market-return assumption should not be entered as a real return without adjusting for inflation. Investment fees and taxes can further reduce growth and are not deducted automatically.
The withdrawal rate is a scenario, not a promise
A target based on spending divided by a withdrawal rate does not prove that a portfolio will last. Retirement length, asset allocation, market sequence, taxes, fees, healthcare, pensions, benefits, future income, spending flexibility, and location can all change the required amount.
Smooth compounding hides market sequence
The calculation applies one constant annual rate. Actual returns vary and may be negative for long periods. Reaching the same average return through a different sequence can produce a different lived outcome, especially when contributions or withdrawals occur. Test lower real returns, higher spending, later or earlier retirement, and lower withdrawal rates.
Compare the gap rather than treating it as a deadline
If current invested savings are below the Coast FIRE number, the displayed gap is the additional balance needed today under the selected assumptions. It is not a required immediate deposit. If savings exceed the number, the surplus only describes this mathematical scenario and is not evidence that contributions should stop.
How this differs from the regular FIRE calculator
The FIRE Calculator projects ongoing monthly contributions until a financial independence target is reached. This Coast FIRE tool instead asks whether today’s balance alone could grow to a target by a chosen retirement age. Use both to understand the difference between active saving and passive compounding.
This educational projection is not investment, retirement, tax, legal, or financial advice. It does not predict returns or guarantee that assets will reach or sustain the target. Verify assumptions, test adverse scenarios, and consider qualified guidance before changing contributions or retirement plans.