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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

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Market assumptions

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Coast FIRE Results

Ready to calculate!

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

1

Enter your current age and target retirement age.

2

Enter current retirement savings and expected annual spending.

3

Set expected return (7% default), inflation (3% default), and SWR (4% default).

4

Click Calculate and compare your savings with the coast number.

5

Check 'years to coast' to see how long savings must grow.

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See the worked examples in the Content Hub for age-30, age-40, and lean-spending scenarios.

Data Sources & References

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Coast number = (spending ÷ SWR) ÷ (1+r)^n

Mathematical Definition

Present value of the retirement target at real return r over n years.

Personal finance practice
Established

r_real = (1+r_nominal)/(1+inflation) − 1

Mathematical Definition

Fisher-style real return conversion.

Classical finance
Established

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SEC compound interest guidance

Guidance

Investor education on compounding and return assumptions.

U.S. SEC
Official

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Retirement withdrawal rate studies ('Trinity Study')

Research

Historical basis for the 4% safe withdrawal guideline.

Trinity University
Peer reviewed

Safe withdrawal rate series

Research

Modern sequence-of-returns analysis for early retirees.

Early Retirement Now
Widely cited

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.

Inputs:
Current age, target retirement age, current retirement savings, expected annual retirement spending, expected annual return, expected inflation, and safe withdrawal rate.
Outputs:
Coast FIRE number, coasting status, target and projected nest egg, required real growth rate, growth multiple versus current savings, years of saving to reach coast, and step-by-step derivation.
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