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FIRE Calculator UK
Estimate your financial independence number, current gap, years to FIRE and possible FIRE age using annual spending, invested assets and monthly investing.
Financial independence target
Years to FIRE
Withdrawal-rate based
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Calculate your FIRE target
Enter your annual spending target, invested assets, monthly investing amount, expected return and withdrawal rate.
The yearly income you want your portfolio to support.
Invested assets that count towards FIRE.
Amount you expect to invest each month.
Use real return if you want to allow for inflation.
Used to calculate the FIRE number.
Used to estimate possible FIRE age.
How to use this calculator
- Enter the annual spending you want your portfolio to cover.
- Add your current invested assets and monthly investment amount.
- Choose an expected return and withdrawal rate.
- Review your FIRE number, current gap and estimated years to FIRE.
What your FIRE result means
Your FIRE number is the investment pot that could support your target annual spending using your chosen withdrawal rate.
The years to FIRE estimate shows how long it may take your current invested assets and monthly investments to reach that target, assuming the return stays constant.
Important: FIRE calculations are planning estimates. Investment returns, inflation, tax, fees and spending needs can all change.
Build the plan behind the FIRE number
Compare your FIRE result with pension, ISA, net worth and emergency fund calculators to see whether the wider plan is balanced.
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How FIRE works
FIRE stands for Financial Independence, Retire Early. The basic idea is to build enough invested assets that your portfolio can support your living costs without relying on full-time work.
The calculator starts with your annual spending target. It then divides that spending by your chosen withdrawal rate. For example, £30,000 of spending at a 4% withdrawal rate gives a FIRE number of £750,000.
The withdrawal rate is not a guarantee. It is a planning shortcut. Your real result will depend on market returns, inflation, tax, fees, account types, spending changes and how long the money needs to last.
Many UK FIRE plans use a mix of pensions, ISAs and taxable investments. A pension may be efficient for later retirement, while an ISA can provide more flexible access before pension age.
What affects your FIRE timeline
- Annual spending: higher spending increases the FIRE number.
- Withdrawal rate: a lower withdrawal rate increases the target but may be more conservative.
- Current investments: a larger starting portfolio reduces the gap.
- Monthly investment: higher monthly investing usually shortens the timeline.
- Expected return: higher assumed returns reduce the timeline, but may be less reliable.
- Inflation: if you use nominal returns, inflation may make the target less realistic in today’s money.
- Tax wrappers: pensions and ISAs can affect how efficiently your investments grow and can be accessed.
FIRE calculator formula
The calculator first works out the FIRE number, then simulates monthly investment growth until the target is reached.
FIRE_number =
annual_spending ÷ (withdrawal_rate ÷ 100)
monthly_rate =
expected_annual_return ÷ 100 ÷ 12
Each month:
portfolio = portfolio × (1 + monthly_rate)
portfolio = portfolio + monthly_investment
years_to_FIRE =
first month where portfolio >= FIRE_number ÷ 12
possible_FIRE_age =
current_age + years_to_FIRE
FIRE number example
This table shows how the withdrawal rate changes the target for the same annual spending.
| Annual spending | Withdrawal rate | FIRE number |
|---|---|---|
| £30,000 | 4% | £750,000 |
| £30,000 | 3.5% | About £857,143 |
| £30,000 | 3% | £1,000,000 |
FIRE calculator FAQs
What is a FIRE number?
A FIRE number is the investment pot you estimate you need to cover your annual spending using a chosen withdrawal rate.
How is the FIRE number calculated?
The calculator divides annual spending by the withdrawal rate. For example, £30,000 at 4% gives a FIRE number of £750,000.
Is the 4% rule guaranteed?
No. The 4% rule is only a planning shortcut. Market returns, inflation, tax, fees and retirement length all matter.
Does this calculator include tax?
No. It estimates the investment target before detailed tax planning. ISA, pension and taxable account rules should be considered separately.
What return should I use?
Use a cautious real return assumption if you want to account for inflation. Higher assumptions can make FIRE look closer but may not be realistic.
Key terms used in this calculator
These glossary pages explain the main terms used when planning financial independence.