Coast FIRE Calculator
Enter your contribution years and invested years separately. See your coast number — the moment you can stop contributing forever.
Calculator Inputs
Coast Number
$113.7K
After 10 yrs contributing
Final Value
$834.4K
After 35 total years
Total Invested
$70.0K
Your cash in
Total Gains
$764.4K
Compound growth
Portfolio Growth Over Time
Amber = contribution phase · Teal = coast phase · Grey = amount invested
You invest $500/mo for 10 years, building to a coast number of $113.7K.
You stop contributing and let compound interest grow $113.7K to $834.4K over 25 more years.
For educational purposes only. Past market performance does not guarantee future results. Full disclaimer →
Frequently Asked Questions
What is a Coast FIRE number? +
Your Coast FIRE number is the amount you need invested today so that — without any additional contributions — your portfolio will grow to your target retirement amount by the time you want to retire. Once you hit your coast number, you can "coast" to retirement purely on compound growth.
What is the difference between contribution years and invested years? +
Contribution years are the years you actively invest money each month. Invested years are the additional years your money continues to grow after you stop contributing. This distinction is the core insight of Coast FIRE — your money keeps compounding even after you stop adding to it.
What annual return rate should I use? +
Historically, the US stock market (S&P 500) has returned approximately 10% annually before inflation, or roughly 7% adjusted for inflation. For conservative projections, many Coast FIRE planners use 6–7%. For nominal (non-inflation-adjusted) projections, 8–9% is common. Always use a rate you are comfortable with.
Can I stop contributing entirely after reaching my coast number? +
In theory, yes — once you reach your coast number, your investments should grow to your retirement target without additional contributions. In practice, most people continue to contribute at a lower rate for comfort and to account for uncertainty in market returns.
How is this different from a regular compound interest calculator? +
Standard compound interest calculators treat your investment timeline as a single continuous phase. CoastVest's calculator lets you model two distinct phases: a contribution phase (where you invest monthly) and a coast phase (where contributions stop but money keeps growing). This reveals the dramatic impact of starting early and stopping contributions well before retirement.