12 May 2026 · Retirement Planning
The 4% rule is the most cited number in retirement planning — and one of the most misunderstood. Here's what it actually means and how to apply it to your situation.
The 4% rule says you can withdraw 4% of your portfolio in year one of retirement, increase that amount with inflation each year, and the money will last at least 30 years.
That's it. Three sentences. But those three sentences carry a lot of hidden assumptions, and misunderstanding them is one of the most common retirement planning mistakes.
In 1994, financial planner William Bengen ran a study on historical US stock and bond returns going back to 1926. He asked: what's the highest annual withdrawal rate that would have survived every 30-year period in history — including the Great Depression, the stagflation of the 1970s, and every market crash in between?
The answer was 4.15%, since rounded to 4%.
This was confirmed by the "Trinity Study" in 1998, which tested a range of portfolio allocations and withdrawal rates across rolling 30-year periods and reached similar conclusions.
The 4% rule is a historical observation, not a guarantee. It says that a 4% withdrawal rate has worked in all past 30-year periods. It doesn't guarantee it will work in future ones.
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Run your numbers in RetireGauge →1. A 30-year retirement
Bengen's study used 30-year periods. If you retire at 65, that covers you to 95. If you retire at 55, you need a 40-year horizon — and the 4% rule becomes riskier.
For longer retirements, research suggests dropping the withdrawal rate:
2. A diversified US stock and bond portfolio
Bengen used a 50/50 US stocks and bonds split. Many subsequent researchers have used 60/40 stocks to bonds. The rule is based on US market history specifically — applying it globally adds uncertainty.
3. Inflation-adjusted withdrawals
The 4% is for year one. In year two, you withdraw 4% of the original balance plus inflation. If inflation runs at 3%, your year-two withdrawal is 4.12% of the original portfolio. After 20 years of 3% inflation, your annual withdrawal is 72% larger in nominal terms.
4. You spend it all
The rule assumes you actually spend the full withdrawal amount each year. In practice, many retirees spend less in bad years — which dramatically improves portfolio survival.
State pension and other income
The 4% rule was designed for people withdrawing solely from a personal portfolio. If you receive state pension, Social Security, a defined benefit pension, or rental income, that income reduces how much you need to pull from your portfolio each year.
If you need £45,000/year and £15,000 comes from state/defined benefit sources, your portfolio only needs to generate £30,000/year — a 4% withdrawal from a £750,000 portfolio, not £1,125,000.
Taxes
Different account types — ISA, SIPP/pension, general investment account — are taxed differently on withdrawal. A gross withdrawal of 4% may net you significantly less depending on your tax situation. The 4% rule doesn't model tax.
Fees
If your funds charge 1.5% annual fees (common in actively managed funds), your portfolio needs to grow an extra 1.5% just to stand still. That's a significant drag on a 4% withdrawal strategy.
Sequence of returns
The order of returns matters enormously. A 30% market crash in year two of retirement is catastrophic compared to the same crash in year 20. This "sequence of returns risk" is the biggest practical danger for people using the 4% rule rigidly.
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Run your numbers in RetireGauge →Use it as a starting point, not an endpoint
The 4% rule gives you a rough target: 25x your annual spending. That's a useful benchmark. But adjust it for your situation: retirement age, state pension, other income, and whether you're comfortable with a 5–10% chance of running out of money before you die (which is roughly the historical failure rate of the 4% rule in bad market scenarios).
Build in a buffer
Many financial planners suggest using 3.5% or 3.75% as a starting withdrawal rate, especially for longer retirements. The extra cushion reduces failure probability significantly.
Plan flexible withdrawals
If you can cut spending by 10–15% in a bad market year, your plan's resilience improves dramatically. Think of the 4% rule as the ceiling in good years, not a fixed annual entitlement.
Re-evaluate periodically
Review your withdrawal rate every few years against your remaining portfolio balance and expected lifespan. If markets have done well, your portfolio may be larger than projected — you can spend more. If they've underperformed, adjust earlier rather than later.
The 4% rule is based on US market data. For other countries, the picture is more complex:
The 25x formula (portfolio = annual spending × 25) is the simple version.
For your real number:
Example: £50,000 spending - £12,000 state pension = £38,000 from portfolio × 25 = £950,000
A retirement calculator that models tax, state pension timing, and investment returns gives you a more accurate answer than the raw 25x formula.
The 4% rule remains a widely used benchmark, but some financial planners argue that lower bond yields and higher equity valuations make it optimistic for future retirees. A 3.5% withdrawal rate offers a larger safety margin. The rule is a historical observation — it worked in the past, but is not a guarantee for the future.
4% of £1 million is £40,000 per year. Under the 4% rule, a £1 million portfolio supports £40,000/year of inflation-adjusted withdrawals over a 30-year retirement. Combined with a full UK State Pension of around £11,500/year, that's £51,500/year — well above average UK household spending.
Yes, with caveats. The 4% rule has historically worked for 30-year retirements with a diversified portfolio. But it doesn't account for unusual market conditions, fees, taxes, or longer retirements. Many people use it as a starting framework and build in additional safety margins through lower initial withdrawal rates, flexible spending, or supplementary income.
Higher withdrawal rates increase the probability that your portfolio runs out before you die. Withdrawing 5% historically failed in roughly 15–20% of 30-year scenarios (depending on portfolio allocation). Withdrawing 6% fails in a significant majority of bad-market scenarios. Lower is safer, especially in the early years of retirement.
Use a lower rate (3–3.5%) if you're retiring before 60, have a long life expectancy, or want a high margin of safety. Use 4% if you're retiring at 65+ and have some flexibility in spending. Use a slightly higher rate (4.5–5%) only if you have significant supplemental income (state pension, part-time work) that reduces portfolio dependence, or if you're comfortable with some failure risk.
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