Coast FIRE calculator
Coast FIRE is the point where retirement saving becomes optional: the money already invested will compound to a full retirement pot by your target age with nothing more added. From there you only need to earn enough to live on. See your Coast number today, how far off it you are, and the age you'd cross the line at your current saving rate.
Your numbers
The discounting, step by step
The Coast FIRE idea
Coast number = FIRE number ÷ (1 + return)^years to your target age. Regular FIRE asks when you can stop working; Coast FIRE asks the gentler question of when you can stop saving. Once your invested money will compound to a full retirement pot on its own, every pound of future salary is released for living, and the only job your earnings have left is covering the bills between now and your target age. Time does the rest of the work, which is why the Coast number is so much smaller than the FIRE number when you're young and grows toward it as the runway shortens.
A worked example at 25
Take a 25-year-old aiming to retire at 60 on £25,000 a year. At a 3.5% withdrawal rate the full FIRE number is £714,286. But it isn't needed until 60, and 35 years of growth at 5% above inflation multiplies money roughly five and a half times, so the pot needed today is the full number discounted back: £129,493. Hold that at 25 and the saving is done. With £60,000 invested and £400 a month going in, the calculator above shows the line being crossed at 52: late, because the Coast number itself rises every year the target gets closer. Arrive at the same numbers five years younger and the crossing moves years earlier, which is the honest lesson of Coast FIRE: it rewards money invested early far more than money invested steadily.
The honest caveats
Everything hangs on the real return holding for decades. At 3% instead of 5% the 35-year multiple drops from 5.5 to 2.8 and the Coast number nearly doubles, so treat the slider as a range of futures rather than a dial you set once. A smooth average also hides the bumps: the same average return delivered in a bad order leaves a different pot, and the volatility drag calculator shows how much that costs. Coasting also means arriving at your target age with exactly enough, no margin, at the end of a plan you stopped feeding decades earlier. There is one genuinely helpful UK wrinkle: for a young saver most of the coasting pot sits in pensions anyway, which stay sealed until 57, so the temptation to raid the plan is handled by law. Check the full journey, spending phase included, with the retirement age calculator, and if the question is when you could stop working rather than stop saving, that's the FIRE calculator.
Common questions
What is Coast FIRE?
The point where your existing investments will compound into a full retirement pot by your target age without another penny added. Once past it, retirement saving is optional: your salary only has to cover life between now and then. It answers "when can I stop saving?" rather than FIRE’s "when can I stop working?".
How do I calculate my Coast FIRE number?
Divide your FIRE number (annual spending ÷ withdrawal rate) by growth over the years remaining: FIRE number ÷ (1 + real return)^years to target age. A 25-year-old wanting £25,000 a year from 60 at a 3.5% withdrawal rate needs £714,286 then — but only about £129,500 today if it compounds at 5% above inflation for 35 years.
Should I actually stop saving once I reach Coast FIRE?
Reaching the line means you could, not that you should. The plan then rests entirely on decades of growth arriving as assumed, with no margin at the end and no new money smoothing bad years. Most people treat Coast FIRE as a milestone that removes pressure — proof the foundation is laid — rather than a signal to cancel the direct debit.
These results are estimates for general information only and are not financial advice. Investment returns are not guaranteed — a plan that assumes decades of growth needs reviewing as markets move. Read the full disclaimer.