FIRE vs Coast FIRE: target, starting capital and the missing bridge

Distinguish a retirement spending target from the capital required now to coast without further contributions. Work through consistent, hypothetical numbers.

A FIRE number, a Coast FIRE number and a savings projection answer three different questions. The first converts an entered annual spending gap into an implied portfolio amount. The second discounts a retirement target back to today under a no-contribution growth assumption. The third models additional money paid into the account. Keeping those jobs separate prevents a lower Coast FIRE figure from being mistaken for money available to spend now.

Start with a spending gap

Use 48,000 annual spending and 12,000 annual other income available at the same time. The portfolio gap is 36,000. Dividing by an illustrative 4% withdrawal assumption gives 900,000 in the same purchasing power. At 3.5%, the implied figure is 1,028,571.43. That is a sensitivity calculation, not evidence that either rate will fund an unknown lifetime. Use the FIRE number calculator to record your own assumptions.

Coasting is a no-new-money scenario

For a separate example, set a 1,000,000 real retirement target 10 years away and assume 10% annual real growth. Dividing by 1.1 to the tenth power gives 385,543.29 required now. If that exact deterministic growth occurs and no money is withdrawn, the assumed starting amount reaches the target. Changing real growth to 5% raises required capital now to 613,913.25. The outcome is highly dependent on the input; neither figure is a forecast.

The Coast FIRE tool converts entered nominal growth, an after-growth asset fee and inflation into a real factor. It does not hide fees inside a supplied expected return. Its table puts projected real assets beside required real coast assets at each age.

Why waiting does not automatically fix a shortfall

Under fixed assumptions and no additional saving, both the asset path and the remaining coast requirement evolve at the same real growth factor. Starting below the requirement does not create a magic later age at which the gap vanishes. Additional contributions, lower spending, a later retirement date or different assumptions describe different models. Use retirement savings when you intend to keep contributing.

The bridge that Coast FIRE leaves out

Money earmarked to grow until retirement is not also a source for current living expenses in this model. If someone stops working today, the years before retirement still need cash. A pension beginning later is not equivalent to other income already available from the first retirement year. Keep a separate bridge budget and a separate account-access analysis. These tools do not determine when an account can legally be accessed or calculate benefits.

Turn an estimate into an inspectable record

1. Build a realistic annual expense scope with the annual budget workbook.
2. Write down when each income source actually starts.
3. State whether every amount is current purchasing power or future currency.
4. Compare one changed assumption in scenario B.
5. Export the calculation, including its timing and limitations.

Investor.gov’s lifetime-income overview provides broader retirement context. The arithmetic and invented examples above are AllMarkets models, not a recommendation from the linked publisher.