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✦ Free UK calculator · 2025/26 tax rules

FIRE Number Calculator UK

Most UK FIRE calculators are American calculators with the dollar sign swapped. They give you the textbook 25× number and stop. This one models how UK investors actually decumulate — the bridge fund you need before SIPPs unlock at 57, the State Pension shaving the back end, and the real tax drag on SIPP withdrawals using 2025/26 bands. The number it gives you is the one you can actually plan around.

🔥
Your real UK FIRE number
All figures in today's £. Updates as you type.
You & your goal
years
years
£
Your assumptions
%
%
years
Where your wealth sits today (optional — for progress tracking)
£
£
£
Your real UK FIRE number
£867,000
Total wealth needed at age 55 to fund £35,000/yr (today's £) until age 90
Bridge fund (ISA/GIA)
£212,000
For years before SIPP unlocks
SIPP at access age
£727,000
Inc. PCLS + tax grossup
State Pension worth
£245,000
Equivalent pot you don't need
Target wrapper split at retirement ISA 26% · SIPP 74%
ISA 26%
SIPP 74%
Bridge / accessible (ISA, GIA) Pension (SIPP, workplace DC)
FIRE number across withdrawal rates Lower SWR = bigger pot, more margin
SWR FIRE number Multiple of spend Your progress
Your FIRE progress 14%
£120,000 today, projected to grow to £xxx by age 55. Target: £867,000.
⏳ Early days — but the maths is doable.
Your portfolio needs to reach £867,000 at age 55. Compound growth gets you part of the way; contributions cover the rest.
ⓘ All figures in today's pounds — the calculator works in real (after-inflation) terms. Tax modelling uses 2025/26 UK Income Tax bands (£12,570 PA, 20%/40%/45%) including the 25% PCLS on SIPP withdrawals. Bridge fund assumes a finite drawdown over years before SIPP access; pension pot assumes the safe withdrawal rate as a perpetuity-safe target. State Pension assumes the full new flat-rate amount (£11,973/yr 2025/26) from age 67 unless toggled. This is a planning aid, not personal financial advice — your circumstances may differ.
✦ The full picture

What a FIRE number actually is — and why the UK version is different

Your FIRE number is the total invested wealth required to fund the rest of your life entirely from withdrawals. The textbook answer is the 25× rule: take your annual spending, multiply by 25, and that's your number. £35,000 a year × 25 = £875,000.

The 25× shorthand exists because of the 4% rule: a Trinity Study finding that a 4% withdrawal rate sustained a 30-year retirement across virtually all historical US 30-year periods. 1 ÷ 4% = 25. They're the same thing.

That formula is fine as a starting point, and it's the one nearly every FIRE calculator on the internet stops at. But for a UK investor, it's missing three things, all of which materially change your number.

Textbook FIRE Number
FIRE Number = Annual spending ÷ Safe withdrawal rate
e.g. £35,000 ÷ 4% = £875,000 · or £35,000 ÷ 3.5% = £1,000,000

1. UK pensions are locked until 57 — you need a bridge fund

UK SIPPs and workplace pensions cannot be accessed until age 55, rising to 57 from April 2028, with longer-term plans to track 10 years before State Pension Age. If you want to retire before 57, you cannot draw a pound from your SIPP — every penny of spending between your retirement age and 57 has to come from ISAs, GIAs, or other accessible accounts. That's the bridge fund.

For a 50-year-old retiring on £35,000 a year, the bridge fund is roughly £35,000 × 7 years ≈ £245,000 in accessible accounts, on top of whatever pension pot will fund the post-57 years. Generic 25× rules ignore this entirely. The calculator above models it explicitly and tells you the ISA target separately from the SIPP target.

2. The State Pension is a hidden boost most calculators leave out

The full new State Pension is £11,973 a year for 2025/26, payable from age 67 (rising to 68 between 2044 and 2046 under current legislation). That's not nothing — it's roughly a third of a £35,000/year lifestyle, for life, inflation-linked.

In SWR terms, £11,973 of guaranteed lifetime income is equivalent to a pot of about £342,000 at a 3.5% withdrawal rate. Including it accurately can reduce your FIRE number by £200k–£300k. The standard objection is "what if it's cut?" — fair, but the answer to uncertainty is to model both scenarios, not to ignore one of them. The calculator lets you toggle between Full / Partial / None.

3. SIPP withdrawals are taxed — your gross number is bigger than your net spending

When you take money out of a SIPP after age 57, 25% is tax-free (the Pension Commencement Lump Sum, or PCLS). The remaining 75% is added to your taxable income for the year — so it stacks on top of any State Pension, rental income, dividends, or other taxable income, and is taxed at the standard UK Income Tax bands.

For 2025/26, that means:

For a SIPP retiree wanting £35,000 net per year before State Pension kicks in, the gross drawdown is roughly £38,200, not £35,000. That difference of £3,200 a year — multiplied across decades and grossed up by the SWR — translates to something like £90,000 of extra SIPP pot required just to cover tax. Calculators that ignore this give you a number that will leave you short.

Putting the three together: the real UK FIRE number

The real UK FIRE number is built from three layers, each calculated on its own terms:

Real UK FIRE Number
FIRE = Bridge fund (ISA/GIA, finite years) + SIPP pot (gross-up tax) − State Pension offset
All three pieces calculated in today's money, real returns throughout

The bridge fund is sized to fund you from your retirement age to 57. The SIPP pot is sized to fund you from 57 onwards, gross of tax, but reduced by the State Pension once it kicks in. The headline number is the sum of both, expressed at retirement age.

That's what the calculator above does. Two retirees with identical £35,000/year spending, both at 5% real return and 3.5% SWR, will get materially different FIRE numbers depending on whether they're retiring at 50 or 60. The 60-year-old needs no bridge, gets State Pension within 7 years, and lands at around £700k. The 50-year-old needs a 7-year bridge, longer until State Pension, and lands closer to £950k+. Same lifestyle, different geometry.

Why 4% is probably too high for UK investors

The 4% rule was built on US data — 1926–1995, mostly US large-cap equities and US Treasury bonds, 30-year retirements. Three reasons UK investors should be more cautious:

The current consensus among UK FIRE planners sits in the 3.25%–3.5% range for high confidence. 3.5% is a reasonable default — it gives a pot 14% larger than the 4% rule but with a meaningful margin against bad luck. The sensitivity table above shows you all five rates side by side so you don't have to commit to one.

📊 Cross-check: Bengen's updated work

William Bengen, who first published the 4% rule in 1994, has revised it upward to 4.7% with international diversification and small-cap value tilts, but only for 30-year US retirements. For a UK investor planning a 35–45 year retirement, his original conservatism still applies. 3.5% is a fair default; 4% is the upper bound, not the centre.

How to actually accelerate your FIRE date

Once you have your number, the gap closes through three levers:

✦ How this compares

What other UK FIRE calculators get wrong

Most calculators ranking for "FIRE number UK" today are American calculators — Fioneers, Networthify, Mr. Money Mustache's spreadsheet — with the dollar sign visually swapped to a pound. Here's what they typically miss vs. this one:

Feature Generic 25× rule Most UK calculators This calculator
Bridge-to-57 modelling No No Yes
State Pension as offset No Vague / lump-sum Toggle Full/Partial/None
SIPP tax drag (PCLS + bands) No No 2025/26 bands applied
Withdrawal-rate sensitivity Single rate Single rate 3.0%–4.0% sweep
Real (after-inflation) terms Sometimes Sometimes Yes
Wrapper allocation guidance No No ISA/SIPP target split
UK 2025/26 tax rules No Often outdated Current bands
✦ How the calculator works

Methodology

1
Decompose retirement into three phases
Phase 1: target_age → SIPP_access. Phase 2: SIPP_access → State_Pension_age. Phase 3: State_Pension_age → end. Each phase has different tax treatment and income sources.
2
Size the bridge fund (Phase 1)
Bridge_fund = annual_net_spend × annuity_factor(N, r). Funded entirely from ISA/GIA at zero tax assumption. Where N = years before SIPP unlocks.
3
Size the SIPP-only window (Phase 2)
Solve gross_SIPP such that gross − tax(0.75 × gross) = annual_net_spend, applying 2025/26 UK Income Tax bands. PV at SIPP_access = gross_SIPP × annuity_factor(M, r) where M = years until State Pension age.
4
Size the State Pension years (Phase 3)
Solve gross_SIPP_with_SP such that SP + gross − tax(SP + 0.75 × gross) = annual_net_spend. Pot needed at State Pension age = gross / SWR (perpetuity-safe target).
5
Discount everything back to retirement age
Phase 3 pot at SIPP_access = Phase 3 pot at SP_age ÷ (1+r)^M. Total SIPP at SIPP_access = Phase 2 + Phase 3. Total SIPP at target_age = SIPP_at_access ÷ (1+r)^N.
6
Sum to FIRE number
FIRE_number = bridge_fund + SIPP_at_target. Total wealth required at retirement age, in today's money.
7
Sweep across SWRs
Recompute the whole stack at SWR = 3.0% / 3.25% / 3.5% / 3.75% / 4.0% so you can see the entire SWR sensitivity at once rather than committing to one number.
8
Project current portfolio forward
Current_pot_at_target = (ISA + SIPP + GIA) × (1+r)^(target_age − current_age). Compare against FIRE_number for a progress percentage.
✦ Common questions

UK FIRE Number FAQ

What is a FIRE number in the UK?
Your FIRE number is the total invested wealth required to fund the rest of your life from withdrawals. The textbook formula is annual spending divided by your safe withdrawal rate (so £35,000 ÷ 4% = £875,000). In the UK that figure is incomplete because it ignores three things: SIPPs are locked until age 57, the State Pension reduces what your pot needs to cover from age 67, and SIPP withdrawals are taxed (only 25% is tax-free as PCLS). A real UK FIRE number adjusts for all three.
Is the 4% rule reliable for UK investors?
The 4% rule was built on US data from 1926 to 1995. It assumed a 30-year retirement, mostly US large-cap equities and US Treasury bonds. UK investors typically use 3.25% to 3.5% for a higher confidence level, especially for retirements longer than 30 years. The lower SWR reflects historically lower UK equity returns, currency exposure on global portfolios, and the additional sequence-of-returns risk of long horizons. The calculator above lets you sweep across 3.0%–4.0% to see how your number moves.
How does the bridge-to-57 problem affect my FIRE number?
If you want to retire before age 57 (the SIPP minimum access age, rising to 58 from April 2028), you cannot draw from your SIPP. Every pound of spending between your retirement age and 57 must come from ISAs, GIAs or other accessible accounts. That's the 'bridge fund'. A 50-year-old retiring on £35k/year needs roughly £35k × 7 = £245k accessible before SIPPs open up, on top of whatever pension pot will fund their post-57 years.
Should I include the State Pension in my FIRE calculation?
Many UK FIRE planners exclude it for conservatism, but the State Pension is one of the most under-modelled levers in early-retirement maths. The full new State Pension is around £11,973 a year for 2025/26 starting at age 67. For a £35k/year lifestyle, that's roughly a third of your spending covered for life — equivalent to a £342,000 pot at a 3.5% withdrawal rate. The calculator lets you toggle between None, Partial (around 20 NI years) and Full so you can see the difference.
How is SIPP drawdown taxed in the UK?
When you withdraw from a SIPP after age 57, 25% is tax-free (the Pension Commencement Lump Sum, or PCLS) and the remaining 75% is treated as taxable income on top of any other income for that year. So if you draw £40,000 gross, £10,000 is tax-free and £30,000 is added to your taxable income. After the £12,570 personal allowance, you'd pay 20% on the next chunk and 40% above £50,270. Most UK FIRE retirees can keep total taxable income near or just into the basic rate band, but the tax drag is real and needs to be grossed up — the calculator does this for you using the 2025/26 bands.
What's the right ISA / SIPP split for FIRE in the UK?
Three rules of thumb: (1) If you'll retire at 57 or later, prioritise the SIPP — higher-rate tax relief on contributions plus tax-free growth is hard to beat. (2) If you'll retire before 57, build the ISA bridge first, then layer the SIPP on top. Roughly, the ISA target is annual_spend × bridge_years. (3) Always capture employer pension match before using anything else — it's a 50–100% instant return. The calculator's wrapper allocation panel shows the rough ISA target / SIPP target for your specific bridge.
What real return should I assume for a UK portfolio?
A "real" return is the return after inflation. For a globally diversified equity portfolio, 4–5% real is a common assumption — 5% if you're optimistic, 4% if you're conservative. For a 60/40 stock-bond portfolio, 3–4% real is more realistic. Avoid using nominal 7–8% returns alongside today's spending — they understate the pot you need because they ignore that future spending also inflates. The calculator works entirely in real (after-inflation) terms.
Why is my FIRE number bigger than 25× my spending?
Two reasons. First, 25× assumes a 4% withdrawal rate; if you use 3.5% the multiple is 28.6×, and at 3% it's 33×. Second, the simple 25× rule ignores tax on SIPP withdrawals — to net £35,000 you might need to withdraw closer to £38,000 gross, which means a bigger pot. The calculator can also produce a smaller number if State Pension is included, because that income offsets some of what your pot has to cover.
What is sequence-of-returns risk and how does this calculator handle it?
Sequence-of-returns risk is the danger of a major market drawdown in the first few years of retirement. A 30% fall while you're drawing 4% can permanently impair the pot, even if average returns recover later. The calculator addresses this implicitly by letting you sweep across SWRs from 3.0% to 4.0% — using 3.25% or 3.5% gives a meaningful margin against bad early luck. For a more rigorous view, the WealthR app runs a probabilistic stress test, but for a planning aid, the SWR sensitivity table tells you most of what you need.
What's the difference between the 25× rule and the FIRE number?
They're the same calculation expressed two ways. 25× annual spending = annual spending ÷ 4%. The 25× shorthand was born from the 4% rule. If you change the SWR, the multiple changes — 28.6× at 3.5%, 33× at 3%. The calculator above shows your number at five different SWRs side by side so you don't have to pick a single number to live by.
Does WealthR track this for me automatically?
Yes. The full WealthR app pulls your tracked ISA, SIPP, pension and other investments together, applies your real return and SWR assumptions, and projects your FIRE date with the bridge-to-57 problem and State Pension factored in. It also tracks progress monthly so you can see how each pay period moves your FIRE date earlier. Free to try, takes about five minutes to set up.

One number is helpful. Tracking it monthly is the point.

WealthR's full app calculates your FIRE number from the ISAs, SIPPs and pensions you actually hold — bridge fund modelled, State Pension factored, tax drag applied, all updated as your portfolio moves. It tells you exactly how much each contribution shifts your FIRE date earlier. Free to try, takes about five minutes.

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