Coast FIRE is the point where your existing portfolio, left untouched, will compound into a full retirement fund by your retirement age — no further contributions needed.
The younger you are, the smaller the Coast number: 35 years of compounding does most of the work. Hitting it means contributions become optional — you only need to cover current living costs.
The calculation discounts your FIRE number (25× spending) back to today at your expected real return. It assumes you genuinely leave the portfolio alone until retirement.
The number is a discounting exercise, so it lives or dies on the real return assumed. Coasting at an assumed 7% real and receiving 4% leaves a shortfall that only becomes visible near the end, when there is least time to fix it — which is why a conservative rate matters more here than in almost any other projection.
Coasting also assumes the portfolio is genuinely left alone, and the risk is behavioural rather than mathematical. A pot that is no longer being fed is easier to raid for a car or a renovation, and every withdrawal resets the clock the calculation was built on.
It changes what a job needs to pay rather than removing the need for one. Reaching the number means income only has to cover current living costs, which is what makes a lower-paid or part-time role viable — a different outcome from retiring, and often the more realistic one.
Frequently asked questions
What is Coast FIRE?
The point where your existing portfolio, with no further contributions, will compound into a full retirement fund by retirement age. From there, you only need to earn your living costs.
How is the Coast FIRE number calculated?
Your FIRE number (about 25× annual spending) discounted back to today at your expected real return. The more years until retirement, the smaller today's required amount.
What is the difference between Coast FIRE and FIRE?
FIRE means the portfolio already funds your life — you can stop working. Coast FIRE only means you can stop saving; you still work to cover current expenses.