How to Use the Retirement / FIRE Calculator
The Retirement / FIRE Calculator projects your retirement savings balance at any target retirement age and calculates your FIRE (Financial Independence, Retire Early) number — the total savings you need to live off investment returns indefinitely. It's a complete retirement planning tool in one place.
Enter your current age, current savings, monthly contributions, expected investment return, and desired annual retirement income. The calculator projects your balance year by year, tells you when you'll hit your FIRE number, and estimates how long your savings will last in retirement using the widely accepted 4% safe withdrawal rate.
The 4% rule — derived from the Trinity Study — suggests you can withdraw 4% of your portfolio annually (adjusted for inflation) with high probability that your money lasts 30+ years. Your FIRE number is therefore 25× your annual expenses. Someone needing £30,000/year needs a £750,000 portfolio.
📊 Worked Example
Age 30, £25,000 saved, £500/month contributions, 7% return, retiring at 65 on £35,000/year:
- Projected balance at 65: £1,247,000
- FIRE number (25× £35k): £875,000
- FIRE achieved at age: 57
- Savings last until age: 96+ (4% withdrawal)
Common Use Cases
- ✅ Projecting your pension or retirement account balance at different retirement ages
- ✅ Calculating your FIRE number if you want to retire early
- ✅ Seeing how increasing contributions today dramatically affects your retirement date
- ✅ Understanding if you're on track for retirement with your current savings rate
- ✅ Modelling different investment return scenarios to stress-test your plan
- ✅ Comparing retiring at 55 vs 60 vs 65 and the savings difference required
- ✅ Estimating how long your retirement pot will last at different withdrawal rates
Frequently Asked Questions
What is the FIRE number and how is it calculated?
FIRE stands for Financial Independence, Retire Early. Your FIRE number is the total savings needed to retire, calculated as your annual expenses × 25. This comes from the 4% safe withdrawal rate — if you spend 4% of your portfolio per year, you have a very high chance of never running out of money over 30+ years.
Is the 4% withdrawal rule still valid?
The 4% rule is based on historical US market data from 1926 onwards. In today's environment of lower bond yields and higher valuations, some financial planners suggest using 3–3.5% to be more conservative. Your actual rate depends on your investment mix, time horizon, and flexibility to reduce spending in bad markets.
How much do I need to retire in the UK?
The UK's Pensions and Lifetime Savings Association recommends £37,300/year for a 'moderate' retirement and £59,000 for a 'comfortable' one for a single person. Applying the 25× rule, you'd need £932,500 for moderate or £1,475,000 for comfortable — supplemented by State Pension.
Does State Pension count toward my FIRE number?
Yes. The UK State Pension (currently up to £11,502/year in 2025/26) and US Social Security significantly reduce the portfolio you need. If you'll receive £10,000/year from State Pension and need £35,000/year, your portfolio only needs to cover £25,000/year × 25 = £625,000.
What investment return should I use for projections?
A diversified global equity portfolio has historically returned around 7–9% before inflation. Most planners use 5–7% in real terms (after inflation) for conservative projections. Using 5% gives you a safety margin; if actual returns are higher, you retire earlier or leave a legacy.