What Is Financial Independence?
Financial independence means your investments generate enough to cover your living expenses without you needing to work. You do not have to retire. Plenty of people who hit FI keep working; they just stop having to. The difference matters.
The 4% Rule
One formula does most of the heavy lifting:
FI Number = Annual Expenses × 25
This comes from the Trinity Study, which found that withdrawing 4% of a diversified portfolio each year has historically lasted 30+ years without the portfolio running out. It is not a guarantee, but it is a reasonable starting point.
Worked Example
| Monthly expense | Annual | |----------------|--------| | Rent/mortgage | £12,000 | | Bills & utilities | £3,600 | | Food & groceries | £4,800 | | Transport | £2,400 | | Insurance | £1,200 | | Entertainment | £2,400 | | Everything else | £3,600 | | Total | £30,000 |
FI Number = £30,000 × 25 = £750,000
With £750,000 invested and a 4% withdrawal (£30,000 per year), your money has historically lasted 30+ years. That is the number. Most people are surprised it is not larger.
UK-Specific Considerations
The State Pension is a real factor. The current State Pension is ~£11,500 per year. If you plan to claim it from age 67, you only need your portfolio to cover the gap above that:
- Expenses to cover from investments after 67: £30,000 - £11,500 = £18,500
- Revised FI Number (from 67): £18,500 × 25 = £462,500
That is a materially smaller target. A lot of UK FIRE calculators ignore this, which makes FI look harder than it is.
ISAs make the maths cleaner. Withdrawals from a Stocks & Shares ISA are tax-free. Your 4% withdrawal is the full £30,000 in hand. In a GIA you would need to account for capital gains tax on top, which eats into the real withdrawal rate.
Inflation will erode your spending power. Build in 2-3% annual inflation when projecting. £30,000 today will buy less in 20 years; your target should reflect that.
How Long Will It Take?
Your savings rate is the single biggest lever, ahead of investment returns and fees. This table assumes you start from zero and earn 7-10% on a global equity fund before inflation:
| Savings Rate | Years to FI (starting from zero) | |-------------|------| | 10% | ~46 years | | 20% | ~37 years | | 30% | ~28 years | | 40% | ~22 years | | 50% | ~17 years | | 60% | ~12.5 years | | 70% | ~8.5 years |
Going from a 10% to a 30% savings rate cuts nearly 18 years off your timeline. That is the number worth focusing on, not trying to squeeze an extra percentage point from your fund choice.
Getting Started
- . Calculate your annual expenses. Track your actual spending for 3 months and extrapolate. Do not guess; most people underestimate by 20-30%.
- . Multiply by 25. That is your FI number.
- . Work out your savings rate. (Income - Expenses) / Income.
- . Track your progress. Your net worth relative to your FI number is the only score that matters. Use CoreFi to monitor it automatically.
- . Work both sides. Cutting expenses and increasing income are not competing goals. The fastest path to FI involves both.
The UK FIRE Community
The UK FIRE community is active on r/FIREUK and r/UKPersonalFinance. A few common approaches come up repeatedly:
- Maxing the ISA allowance (£20,000 per year, tax-free growth and withdrawals)
- Capturing the full employer pension match before putting money anywhere else
- Investing in low-cost global index funds (Vanguard FTSE Global All Cap is the most cited)
- Cutting housing costs, which for most people is where the real money is
The maths is simple. The hard part is doing it for long enough.