What Is Coast FIRE? How to Calculate Your Number

Coast FIRE is the point at which you've invested enough that — without adding another penny — compound growth alone will carry you to full financial independence by your target retirement age.

The Coast FIRE formula

Your Coast FIRE number = FIRE Target ÷ (1 + r)^n

• FIRE Target = your annual spending in retirement × 25 (the 4% rule)
• r = expected real annual return (typically 5–7% after inflation)
• n = years until retirement

Example

You want £40,000/year in retirement. FIRE target = £1,000,000. You're 35, want to retire at 60 (25 years). Assuming 6% real returns: Coast number = £1,000,000 ÷ (1.06)^25 = £233,000.

Hit £233k by 35, stop contributing, and your investments reach £1m by 60.

Why it matters

Once you've hit your Coast number, you only need to earn enough to cover living expenses — no need to save for retirement any more. Many people use this as a trigger to downshift careers, go part-time, or start a business.

Find your number with our Coast FIRE calculator.