Coast FIRE Calculator

Find out the portfolio size where you can stop saving entirely and let compound growth carry you to financial independence.

Learn how this calculator works

Your numbers

FI target method

Target FI number

Current age

Target FI age

Expected annual return (7%)

Current portfolio value

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Your Coast FIRE Number

£226,529

If your portfolio reaches this amount, you can stop saving and compound growth will do the rest.

Based on a £625,000 FI target at age 45, with a 7% annual return over 15 years.

Not yet - keep saving

Your current portfolio of £0 is £226,529 short of your Coast FIRE number.

Progress to Coast FIRE0%

How Coast FIRE works

Coast FIRE is the point where your existing investments, left untouched, will grow to your full FI number by your target retirement age through compound returns alone.

The coast number is calculated by discounting your FI target back to today at your expected rate of return. In other words, it answers the question: "How much would I need right now so that 7% annual growth turns it into £625,000 over 15 years?"

The formula is straightforward: Coast Number = FI Target / (1 + r)^n, where r is your expected annual return (7%) and n is the number of years until your target FI age (15).

Once you hit your coast number, any money you earn only needs to cover current expenses. You no longer need to save for retirement, which can free you to take a lower-paying but more fulfilling job, work part-time, or simply reduce financial stress.

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What is Coast FIRE?

Coast FIRE is the point at which your existing investments are large enough to compound into your full retirement target without you ever saving another pound. You still need a job to cover current living costs, but you can stop actively feeding the portfolio. Time and compound returns do the rest.

It sits between two more familiar concepts. Full FIRE (Financial Independence, Retire Early) means your portfolio covers both your present AND your future. You don't need earned income at all. Coast FIRE means your portfolio covers your future, but you still need to work to cover your present. It is the most useful FIRE milestone for most readers because it is reachable a decade or more before full FI.

The Coast FIRE formula

The maths is the simplest in the FIRE toolkit:

Coast FIRE number = FI number / (1 + r)^n

r is your annual real (post-inflation) return as a decimal.
n is the number of years until your target FI age.

If your FI number is £750,000 and you have 25 years to compound at 6% real return, your Coast FIRE number is £750,000 / (1.06)^25 ≈ £175,000. Once you have £175,000 invested, the portfolio will grow to £750,000 by retirement on its own. The calculator above does the maths for you and lets you adjust the inputs to see how the number moves.

Worked examples

Sam, 34, retire at 60, £30,000/year retirement expenses

FI number at 4% withdrawal rate: £750,000
26 years to compound at 6% real return
Coast FIRE number: £750,000 / (1.06)^26 ≈ £164,500
Once Sam hits £164,500 invested, work just has to cover today's bills.

Same Sam, but retiring at 50 instead of 60

16 years to compound instead of 26
Coast FIRE number jumps to: £750,000 / (1.06)^16 ≈ £295,000
Pulling the retirement age forward 10 years nearly doubles the Coast number.

Alex, 25, retire at 65, £40,000/year retirement expenses

FI number at 4%: £1,000,000
40 years to compound at 6%
Coast FIRE number: ~£97,000
A 25-year-old who hits £97k of invested assets is mathematically done with retirement saving, even if it doesn't feel like it.

Why Coast FIRE is the most useful FIRE milestone

Full FIRE is 30 to 40 years away for most readers saving 20% of income. That timeline is hard to stay motivated for, and life rarely cooperates with linear plans. Coast FIRE is reachable in 10 to 15 years for aggressive savers and unlocks a different set of options:

Switch to lower-paid but more meaningful work without derailing retirement maths.
Drop to four days a week. The lost income only has to cover today's expenses, not the retirement target.
Take a sabbatical, retrain, or go back to school. Coast FIRE turns career breaks into decisions about current cashflow only, not catastrophic-for-retirement gambles.
Have a child and lose one income for several years. The portfolio keeps compounding.
Become self-employed. Trade income certainty for autonomy, knowing retirement is funded.

The opinion frame here is worth being explicit about. Coast FIRE is the closest thing in UK personal finance to genuine freedom from the labour market while you are still working. It does not free you from work entirely, but it removes the financial threat that keeps most workers stuck in roles they would otherwise leave. Hitting it earlier is the single highest-leverage thing a mid-career worker can do for their own bargaining power.

UK-specific considerations

Two adjustments to the standard Coast FIRE calculation are worth thinking about as a UK investor.

First, the State Pension reduces what your portfolio has to cover from State Pension age onwards. If your annual expenses are £30,000 and you'll get the full £12,000/year State Pension from 67, your portfolio only needs to fund £18,000/year from that point. That reduces your FI number, which reduces your Coast FIRE number. The FI number calculator handles the State Pension adjustment; feed the resulting number into this calculator.

Second, the typical UK real-return assumption is slightly lower than US-centric Coast FIRE calculators suggest. UK and global equities have returned around 5% real over long windows; US-only equities have returned roughly 7%. If you hold a global tracker like Vanguard FTSE Global All Cap, 5% real is the prudent base case. The calculator's default of 6% sits in the middle of the range; drop it to 5% if you want a more conservative plan.

Frequently asked questions

What is Coast FIRE in simple terms?

Coast FIRE is the portfolio size that, left alone with no further contributions, will compound to your full FI number by your target retirement age. You still need a job to cover today's living costs, but you can stop saving for retirement entirely. It is reached years - often a decade or more - before full FIRE.

How is the Coast FIRE number calculated?

Coast FIRE = FI number divided by (1 + r)^n, where r is your annual real return as a decimal and n is the number of years until your target FI age. For a £750,000 FI target with 25 years to compound at 6% real return, the Coast FIRE number is about £175,000.

What return assumption should I use?

For a globally diversified UK investor holding a fund like Vanguard FTSE Global All Cap or HSBC FTSE All-World, 5% real return is the conservative case and 6% is the middle case. US-only portfolios have historically returned around 7% real but UK investors should not assume that continues. Use 5% if you want a buffer, 6% for the default plan.

Should I include my pension in the current portfolio?

Yes. Coast FIRE only works if you count all your invested assets - ISAs, SIPPs, workplace pensions, and any other long-term investments. Exclude your emergency fund, current account, and any cash you would not invest. Your home does not count either since you cannot draw an income from it without selling.

Does the State Pension affect my Coast FIRE number?

Yes, indirectly. The State Pension reduces what your portfolio has to fund from age 66/67 onwards, which lowers your FI number, which lowers your Coast FIRE number. Use the FI number calculator to factor in the State Pension first, then feed the resulting FI figure into the Coast FIRE calculation.

Can I still save after reaching Coast FIRE?

Of course. Coast FIRE means you no longer need to save to hit your target. It does not mean you should stop. Most people who hit Coast FIRE keep saving for a while as a buffer against lower-than-assumed returns, or to pull their retirement age forward, or to give themselves the option of a lower-income job. Coast FIRE is a floor on your flexibility, not a target you stop at.