UK FIRE Calculator
A UK FIRE calculator works out how much you need invested to retire early in the UK, and when you can do it — accounting for the things US calculators miss: the gap before you can access your SIPP at 57, the order you draw from your ISA vs SIPP, and UK tax on withdrawals. As a rule of thumb, on a 4% safe withdrawal rate a £40,000/year retirement needs roughly £1.08M — but your real number depends on your tax wrappers and how long you must bridge to pension age.
How much do I need to retire early in the UK?
The classic starting point is 25× your annual spending (a 4% safe withdrawal rate). But that assumes your withdrawals are untaxed. In reality, money drawn from a General Investment Account is subject to Capital Gains Tax, and pension income is taxed — so the pot you actually need is a little higher. These figures are computed with the same engine the calculator uses (UK, 4% SWR, taxable account, in today's money):
| Target spending (after tax) | Portfolio you need |
|---|---|
| £30,000 / year | £0.81M |
| £40,000 / year | £1.08M |
| £50,000 / year | £1.36M |
| £60,000 / year | £1.63M |
| £80,000 / year | £2.19M |
Hold more in an ISA and the number falls toward a clean 25×, because ISA withdrawals are tax-free. Model your own split, tax wrappers and drawdown order in the calculator.
The bit US calculators get wrong: the bridge to 57
If you retire before you can access your pension, you have a bridge period to fund entirely from ISAs and taxable accounts. From April 2028 the earliest you can normally touch a SIPP or workplace DC pension is age 57 (it's 55 until then). Retire at 50 and that's a seven-year gap where your pension is locked and your investments do all the work. Getting the bridge wrong is the single most common UK early-retirement mistake — so InflectionFI models it phase by phase, rather than treating your wealth as one undifferentiated pot.
ISA vs SIPP: which do you spend first?
Broadly: your ISA is tax-free and accessible at any age — ideal for the bridge years. Your SIPP gives 25% tax-free and the rest is taxed as income, and is locked until 57. So most UK early retirees spend taxable accounts and ISAs first to bridge, then layer in the SIPP (using the personal allowance and 25% tax-free element efficiently) once it unlocks. The right order depends on your numbers — the calculator sequences it for you and shows the tax at each stage.
Model your own numbers — ISA/SIPP split, the bridge to 57, Monte Carlo and more.
Open the free UK FIRE calculator →Frequently asked questions
How much do I need to retire early in the UK?
As a rule of thumb, 25× your annual after-tax spending (a 4% safe withdrawal rate). For £40,000/year that's about £1.08M once UK tax on withdrawals is accounted for. Holding more in an ISA lowers the figure because ISA withdrawals are tax-free.
At what age can I access my pension in the UK?
The normal minimum pension age is 55, rising to 57 from 6 April 2028. If you retire earlier, you must "bridge" the gap with ISAs and taxable accounts until your SIPP or workplace pension unlocks.
What is a safe withdrawal rate in the UK?
Many UK FIRE plans use 3.25%–4% depending on how conservative they are and how long the retirement is. A lower rate needs a bigger pot; the calculator lets you set the rate and stress-tests it with Monte Carlo simulation and historical backtests.
Should I withdraw from my ISA or SIPP first?
Usually ISAs and taxable accounts first (they are accessible before 57 and the ISA is tax-free), then the SIPP once it unlocks — using the 25% tax-free element and personal allowance efficiently. The best order depends on your figures, which the calculator works out.
Is InflectionFI free?
Yes — the core UK FIRE calculator is free to use. Advanced tools (Monte Carlo, historical backtests, the bridge analysis and AI insights) are available on paid tiers.
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InflectionFI is an educational planning tool, not financial or tax advice. Figures are estimates based on your inputs and stated assumptions. Verify your situation with a qualified adviser.