Financial independence

Coast FIRE calculator

Coast FIRE is reached when the portfolio already invested can plausibly grow to the retirement target by the retirement age without additional contributions.

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# Coast FIRE checkpoint
current_age = 35
retirement_age = 65
current_portfolio = 120000 in usd
annual_spending = 40000 in usd
return_rate = 7%
inflation_rate = 2%
withdrawal_rate = 4%
retirement_target = annual_spending / withdrawal_rate
years_to_retirement = retirement_age - current_age
real_return = (1 + return_rate) / (1 + inflation_rate) - 1

Inputs

What the model needs

Current age: The starting age for the compounding horizon.
Retirement age: When the portfolio is expected to support spending.
Current portfolio: Invested assets assigned to retirement.
Annual spending: The real spending target at retirement.
Return, inflation, withdrawal: The assumptions connecting today’s balance to the future target.

Method

Formulas stay visible

retirement_target = annual_spending / withdrawal_ratereal_return = (1 + nominal_return) / (1 + inflation) - 1coast_number_today = retirement_target / (1 + real_return)^(retirement_age - current_age)

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Worked example

Thirty years for the portfolio to compound

Age 35 today
Retirement at 65
$120,000 portfolio
$40,000 annual spending
4% withdrawal assumption

ResultThe retirement target is $1,000,000 in real spending terms.

Whether $120,000 is enough to coast depends on the real return over three decades. A modest assumption change can move the checkpoint by years.

Stress-test it

Test retirement several years earlier and later.
Lower the real return instead of relying on a single historical average.
Increase annual spending to include taxes, healthcare, and housing changes.

Use it when

Exploring whether retirement saving could slow later
Comparing more contributions now with a longer working horizon
Separating retirement security from full early retirement

Know the boundary

Coast FIRE does not mean current living expenses are funded.
The model does not guarantee returns or a safe withdrawal rate.
Contribution changes should be considered alongside emergency savings and other goals.

Questions

How is Coast FIRE different from FIRE?

FIRE means the portfolio is modeled to support current spending now. Coast FIRE means it may grow to the future target by retirement without new contributions.

Do I stop investing at Coast FIRE?

The calculation identifies a modeled checkpoint, not an instruction. Continuing contributions adds margin and can absorb weaker returns or changing goals.

Why use real return?

The spending target is expressed in purchasing-power terms, so growth must be adjusted for inflation to stay comparable.

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Coast FIRE calculator

What the model needs

Formulas stay visible

Stress-test it

Use it when

Know the boundary

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