Coast FIRE calculator

How to use the Coast FIRE calculator

1. Under You, enter Your age, the Age you want to stop working, what you have Invested now and what you’re Investing each month until you coast.
2. Under Retirement, enter Yearly spending in retirement (today’s money), then check the Withdrawal rate (4% to start with) and Return after inflation (5%).
3. If a state pension or Social Security will pay part of your costs, switch on that toggle and enter the yearly amount and the age it starts.

The result shows your Coast FIRE number today and your full FIRE number at the age you stop. It also shows how far you are from coasting, what you’d have at that age if you stopped investing today, and the age you could stop at your current monthly amount. The table under the chart gives the same figures year by year.

How the numbers are worked out

Your FIRE number is your yearly spending in retirement divided by the withdrawal rate. The Coast FIRE number is the amount that would grow into it by your stop age with nothing added:

Coast FIRE number = FIRE number ÷ (1 + r)ⁿ

Here r is the return after inflation and n the years until you stop working. For the age you could stop investing, the calculator steps forward a month at a time, adding your monthly amount, and finds the first month where the pot, left alone, would still reach the FIRE number in time.

The defaults are age 30, stopping at 60, spending of 40,000 a year, 50,000 invested and 1,200 a month, in whichever currency you pick. The FIRE number is 40,000 ÷ 0.04 = 1,000,000. Over 30 years at 5%, money grows 1.05³⁰ = 4.322 times, so the coast number is 1,000,000 ÷ 4.322 = 231,377. You’re 181,377 short, and left alone your 50,000 would reach 216,097 by 60.

At 1,200 a month you could stop investing at about 50 and let growth carry the pot to 1,000,000 by 60. At 1,500 a month that age falls to about 44. At 800 a month you’d never get there: even investing every month until 60, the pot reaches about 868,000, so the result reads “not before 60”.

Coast FIRE next to the other kinds

Full FIRE means having enough invested that withdrawals could pay your bills now, and the FIRE calculator works out that number and how long it takes. Coast FIRE is a stage on the way. You keep working, but your pay only has to cover today’s spending, because the pot finishes growing on its own. Barista FIRE sits in between: part-time pay covers some costs while the pot covers the rest. Lean and Fat FIRE describe the budget (smaller or larger) rather than the route.

Coasting has a cost. Every year you don’t invest, the plan leans entirely on the return you assumed, and any shortfall shows up late, when there’s little time left to fix it.

How much the return changes the answer

Two points either side of the default change the answer more than threefold: 411,987 at 3% against 131,367 at 7%. Fees do the same. A 0.5% yearly fee comes straight off the return, and at 4.5% the coast number is 267,000.

The age you stop moves it as well. At 5%, stopping at 55 needs 295,303 at age 30 and stopping at 65 needs 181,290; each five years later cuts the number by about a fifth, because 1 ÷ 1.05⁵ = 0.78. The cost of waiting calculator shows the same effect at the other end: what starting five years later costs.

Use a return after inflation

The FIRE number is in today’s money, so the return has to be after inflation too. Say you expect 7% a year before inflation, with inflation at 2.5%: the real return is 1.07 ÷ 1.025 − 1 = 4.39%, and the coast number for 1,000,000 at 60 is 275,551. Enter 7% instead and you’d get 131,367. That’s less than half.

The two only agree if you also turn the target into future money. Spending of 1,000,000 in today’s money is 2,097,568 after 30 years of 2.5% inflation, and 2,097,568 ÷ 1.07³⁰ = 275,551, the same answer.

State pensions, Social Security and pension ages

Income that starts later lowers the coast number. The pot only covers the spending that income doesn’t, plus the years between stopping work and the income starting.

Say Aisha is 30, lives in Manchester and wants to stop work at 57, the age UK private pensions open from 6 April 2028. She expects to spend £28,000 a year and has £50,000 invested, adding £600 a month. With no state pension entered, her FIRE number is £700,000 and her coast number today is £187,494. At £600 a month she doesn’t get there before 57.

The full new State Pension is £241.30 a week in 2026/27, or £12,547.60 a year, and for someone her age State Pension age is 68 under current law (DWP). With it switched on from 68, her pot has to cover £15,452.40 a year for life (£386,310 at 4%) plus the State Pension’s share for the 11 years from 57 to 68 (£104,226 at 5%). Her FIRE number falls to £490,536 and her coast number to £131,389. At £600 a month she could stop investing at about 46½.

Risks to the plan

• Returns arrive unevenly. Markets don’t deliver the average every year, and a fall in the years before you stop work leaves little time to recover. At 3% instead of 5%, the coast number is 78% higher.
• Spending creeps up. A budget 10% bigger, 44,000 a year, means a 1,100,000 target and a coast number of 254,515.
• Rules change. The UK minimum pension age is already rising from 55 to 57, and State Pension age is reviewed regularly.
• Employer money can stop too. If your employer only pays into your pension while you do, coasting can mean giving up its contributions as well.

Scroll is education, not advice. Our lessons and calculators explain how money works in general. They don’t know your circumstances, so they can’t tell you what to do with yours. For that, speak to a qualified, regulated adviser in your country.