Coast FIRE UK: Have You Really Hit Your Number?

The coast-FIRE calculators online mostly do the same thing. They take your retirement target, discount it back to today, and tell you the pot that would grow into it on its own. Hit that number and you can, in theory, stop saving and let compounding finish the job. What almost none of them tell you is the part that decides whether the plan actually holds: the withdrawal rate baked into the number, and whether a UK pot is even reachable at the age you want to stop.

This guide covers the two things the generic tools leave out, both drawn from where UK savers actually get caught. Round numbers are used in the examples to keep them easy to follow - your own figures go in the tool below.

What "Coast FIRE" Actually Means

Coast FIREThe point where your existing pot, left alone, compounds to your retirement target by your chosen age with no further saving - you keep working for income but stop contributing. Maths: target discounted back at your expected real return. is the point where your existing pot, left completely alone, is projected to grow into your retirement target by the age you choose - so you keep working to cover today's spending, but you stop adding to the pot. The arithmetic is a present-value calculation: take your FIRE number - the pot that funds your annual spending at a chosen withdrawal rate - and discount it back to today at the real growth rate you expect.

Two rules make or break that sum, and both are consensus, so we will not dwell on them. Work in real terms, after inflation, not nominal: subtract your inflation assumption from your headline return before you discount, or you will overstate the pot you already have and think you are closer than you are. And use an honest withdrawal ratesafe withdrawal rate (SWR): The share of a portfolio you draw in year one of retirement, uprated with inflation, that research suggests survives a full retirement. The 4% rule is US data; UK estimates run from 3.1% to 4.1%, and none of them models a pension pot.. The widely quoted 4% rule comes from US market research, popularised by the Trinity Study; UK-focused work tends to land lower, which is why the tool defaults to 3.5% and lets you test 3.0% and 4.0% against it.

The Withdrawal Rate Hidden Inside Your Coast Number

Reaching your coast number is necessary. It is not sufficient. The number is only as safe as the withdrawal rate you built it on, because your FIRE number is your annual spend divided by that rate. Assume you can draw 6% and the target shrinks, so the pot looks reached far sooner. Assume a sustainable 3.5% and the same spending needs a much larger pot - and you are further from coasting than the optimistic version claimed.

This is the error the FIRE community corrects again and again: a coast number resting on a draw nobody would actually risk. The tool shows the implied withdrawal rate your own inputs produce - your spend divided by the pot the coast path delivers at your target age - so you can see whether your "coast" sits on a rate you could really live on, or only looks reached because the maths assumed too much.

A Coast Pot Inside a Pension Does Not Pay for the Early Years

The US framing has one more blind spot for a UK saver: the access wall. Money inside a pension or SIPPSelf-Invested Personal Pension: A personal pension you control, choosing your own investments. Growth inside it is free of UK tax; withdrawals are taxed as income from age 55 (57 from 2028). is locked until the normal minimum pension agenormal minimum pension age (NMPA): The earliest age you can normally take a private pension. It is 55 now and rises to 57 on 6 April 2028. Protected pension ages, uniformed-services schemes and ill-health access are the exceptions. - 55 now, rising to 57 from 6 April 2028 under section 10 of the Finance Act 2022. If you want to stop working before then, a pot that is mostly pension has "coasted" to a number you cannot yet touch. (You may see "58" quoted elsewhere - that is wrong; the legislated age is 57.)

What fills the gap is your accessible money - ISAIndividual Savings Account: A tax-free wrapper. Gains and income on investments held inside an ISA are free of Capital Gains Tax and dividend tax. The annual subscription allowance is £20,000. and general investment account savings - drawn down until the pension unlocks. Size it as the years to your access age multiplied by your annual spend. The tool takes the pension share of your pot, grows the accessible part on its own, and shows the bridge shortfall directly, so a locked-up "coast" does not read as a finished one. For the wrapper-order arbitrage and the 2028 cliff read by your birth date, see our guide to retiring before 57.

Plan for the Age, Not the Headline Number

Access-age anxiety is the real UK worry here, ahead of tax. People plan for 58, 60, or "whenever they move it again", not the legislated 57 - and that caution is reasonable, because the age has already been moved once. The practical answer is not to guess a single future age but to keep the bridge flexible: the larger your accessible pot relative to your pension, the less a later access age can hurt you. Model a couple of target ages in the tool and watch what the bridge shortfall does.

Being Able to Coast Is Not the Same as Choosing To

Even where the numbers say you can stop contributing, UK tax often says you should not. Higher-rate pension relief and an employer match are among the best returns available, so the common advice is the opposite of the coast instinct: keep funding the pension and spend down the ISA instead. Coasting can be mathematically available and still the wrong move - our guide to how long a pension pot lasts covers the decumulation side, including sequence-of-returns risksequence-of-returns risk: The risk that the order of investment returns, not their average, decides the outcome once you are withdrawing. Early losses force you to sell more units at low prices to raise the same cash, and those units are gone when markets recover..

One variant is worth naming in passing: Barista FIRE, where part-time income covers your spending while the pot coasts untouched - a middle path between coasting on and fully stopping.