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Coast FIRE calculator

The short answer: your Coast FIRE number is your retirement target discounted by growth back to today. Have that much invested and compounding alone finishes the job by retirement age; contributions become a choice, not a sentence. This tool shows your number, your gap, and the age the lines cross.

Your age30

Retirement age65

Annual spending in retirement£24,000/yr

Withdrawal rate you trust4%

Invested so far£40,000

Investing per month£600/mo

Assumed growth5%

Use a real (after-inflation) figure if your spending number is in today's money. 5% real is already optimistic; the classic planning range is 3 to 5%.

Your Coast FIRE number today

£108,774

Gap to coast

£68,774

Full retirement target

£600,000

Coast age at current saving

Your pot (still contributing) Coast threshold at each ageage 30 to 65

Where the lines cross is your coast age: from there, compounding alone carries the pot to your target by 65. Two honest notes. Coast FIRE quietly assumes you never touch the pot and never suffer a decade of flat returns at exactly the wrong time; a margin above the threshold is not paranoia, it is the plan surviving contact with markets. And coasting is a spectrum, not a cliff: cutting contributions in half at the crossover is often the saner move than stopping cold.

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Educational information, not financial advice. Figures current as of July 2026 where dated; allowances and rates change, so check the source before acting.