I've thought about this question carefully and found that the answer is more specific to individual circumstances than most generalist guidance acknowledges — and the specifics change the number significantly.
Net worth is a simple calculation: everything you own minus everything you owe. What is not simple is knowing what number you are actually aiming for. Most people have a vague sense that more is better, but no target. Without a target, saving feels open-ended and progress feels invisible. Here is how to set a specific number based on how you actually want to live.
Defining Financial Independence
Financial independence means your investment portfolio generates enough passive income to cover your living expenses without you needing to work. At that point, work becomes optional. This is the practical definition — not retirement at a specific age, not a round number like "a million pounds," but the point where your assets produce enough to sustain your lifestyle indefinitely.
The threshold depends entirely on your annual spending. Someone who spends £20,000 per year needs a different portfolio than someone who spends £60,000 per year. This is the first number to establish: not what you earn, but what you spend — or intend to spend once you stop working.
Income vs Net Worth
Income and net worth are related but not the same thing. High earners who spend almost everything they make accumulate little net worth. Moderate earners who invest consistently over decades accumulate substantial net worth. The variable that connects income to net worth is the savings rate — the percentage of take-home pay that is not consumed.
A person earning £80,000 and spending £75,000 has the same savings rate as a person earning £40,000 and spending £37,500 — both save 6.25% of income. They will accumulate net worth at similar rates relative to their spending level. The higher earner will accumulate more in absolute terms, but will also need more at retirement because their expenses are higher.
This is why financial independence planning focuses on spending, not earning. Your required net worth is a multiple of your annual spending, not your annual income.
The 4% Rule
The 4% rule is the standard framework for calculating a retirement portfolio target. It states that a diversified investment portfolio can sustain annual withdrawals of 4% of its initial value indefinitely, based on historical market returns over 30-year periods.
Applied as a target calculation: multiply your desired annual spending by 25. That is the portfolio required to sustain it at a 4% withdrawal rate.
- £20,000/year spending: target portfolio of £500,000
- £35,000/year spending: target portfolio of £875,000
- £50,000/year spending: target portfolio of £1,250,000
- £70,000/year spending: target portfolio of £1,750,000
These numbers include all income sources in retirement. If you expect £10,000/year from the State Pension, your portfolio only needs to cover the remaining spending gap. A person spending £35,000 and receiving £10,000 State Pension needs a portfolio producing £25,000/year — a target of £625,000, not £875,000.
Adjusting for Your Situation
The 4% rule is a starting point, not a precision tool. Several factors push the appropriate rate lower (meaning a larger target portfolio):
Longer retirement: The 4% rule was derived for 30-year retirements. Retiring at 50 and potentially living to 95 requires a more conservative withdrawal rate — 3% to 3.5% — which means a target portfolio 29 to 33 times annual spending rather than 25 times.
Higher spending volatility: If your spending includes large irregular costs — healthcare, property maintenance, travel — the average may understate peak spending years. Building in a buffer reduces sequence-of-returns risk.
UK-specific factors: The 4% rule is based on US market data. UK equity returns have historically been slightly lower, which some analysts argue supports a 3.5% withdrawal rate. The State Pension and potential defined benefit pension entitlements reduce the required portfolio, partially offsetting this.
How to Use the Calculator
The Net Worth Target Calculator takes your target annual spending, any expected income in retirement (State Pension, defined benefit, rental income), and your chosen withdrawal rate, and calculates the portfolio required to cover the gap. It also shows how long it will take to reach that target from your current net worth at different savings rates.
Start with your current monthly spending. Adjust for any costs that will disappear in retirement (mortgage payments, commuting, work clothing) and any that might increase (healthcare, leisure). The result is your retirement spending target — and from that, your net worth target falls out of simple arithmetic.