Coast FIRE Calculator UK: Have You Saved Enough Yet?

Coast FIRE is the point where the money you have already invested will grow into your full retirement pot on its own, even if you never add another pound. Past that point you only need to earn enough to cover today's bills. This calculator works out your Coast FIRE number, tells you whether you have reached it, and if not, how much you would need to save each month to get there by the age you choose. The earlier you hit it, the smaller it is, because compounding does more of the work.

How the Coast FIRE number is worked out

Your full retirement target is the pot you need on the day you stop work. If you set it from spending, the calculator divides the yearly income by your withdrawal rate, so £25,000 at 3.5% needs about £714,000. Your Coast FIRE number is that target discounted back to today at your expected return: target ÷ (1 + return)^{years to retirement}. At 4% a year with 25 years to go, every £1 needed at retirement needs about 38p invested today.

If you are short, the calculator also tells you two things. First, the age at which your current pot, left untouched, would grow to the full target: the earliest you could retire without adding to it. Without new money you never catch up with the Coast FIRE number before your chosen retirement age, because the pot and the number grow at the same rate. Second, the monthly amount you would need to invest, at the end of each month, to reach Coast FIRE by the age you picked. After that age you could stop contributing and still arrive at your target on time, if returns match your assumption.

What it does not cover

• Returns are not smooth. The maths assumes the same return every year. Real markets jump around, and a bad run just before you retire matters more than one early on. Treat the number as a checkpoint, not a finish line.
• Pension access. Money in a pension cannot normally be drawn until the minimum pension age. If you want to retire earlier, you need enough in ISAs or other accounts to bridge the gap.
• Tax. Pension income above the 25% tax-free part is taxed as income, so a pension-heavy pot buys less spending than an ISA pot of the same size. Our pension withdrawal tax calculator shows the difference.
• Real versus nominal. Enter a return after inflation and keep your spending in today's pounds. Mixing a nominal return with today's spending will make the number look smaller than it really is.

To check your full target first, use the retirement number calculator, and to see how long a regular saving plan takes to get there, try how long to reach an investment target.