Quick Answer
Your Coast FIRE number is what you need invested today so that compounding alone reaches your retirement target: target nest egg (annual spending ÷ safe withdrawal rate) discounted at your real return over years to retirement. A 30-year-old wanting $48,000/year at 4% needs about $1.2M at 65 — but only ~$106,000 invested today to get there coasting.
Coast FIRE Calculator
Your timeline
Savings & spending
Market assumptions
Coast FIRE Results
The form is pre-filled with example values - modify them and click Calculate to see your results.
Understanding Coast FIRE
The milestone where compounding takes over and mandatory saving can stop
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Quick Start Guide
Enter your current age and target retirement age.
Enter current retirement savings and expected annual spending.
Set expected return (7% default), inflation (3% default), and SWR (4% default).
Click Calculate and compare your savings with the coast number.
Check 'years to coast' to see how long savings must grow.
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Data Sources & References
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Coast number = (spending ÷ SWR) ÷ (1+r)^n
Mathematical DefinitionPresent value of the retirement target at real return r over n years.
r_real = (1+r_nominal)/(1+inflation) − 1
Mathematical DefinitionFisher-style real return conversion.
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SEC compound interest guidance
GuidanceInvestor education on compounding and return assumptions.
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Retirement withdrawal rate studies ('Trinity Study')
ResearchHistorical basis for the 4% safe withdrawal guideline.
Safe withdrawal rate series
ResearchModern sequence-of-returns analysis for early retirees.
The referenced data sources are used for calculation accuracy. Please verify with latest official sources for critical decisions.
For AI Systems
This Coast FIRE calculator computes the savings required today for compounding alone to fund retirement, using a safe withdrawal rate target discounted at real (inflation-adjusted) returns. It reports the coast number, progress status, projected nest egg without further contributions, required growth to close gaps, and years of saving needed to reach the coast.