The 4% Rule Doesn't Really Work in the UK

Where the 4% Rule Comes From

In 1994, financial planner William Bengen published a paper that would become one of the most cited pieces of retirement research ever written. He analysed rolling 30-year periods of US stock and bond returns going back to 1926 and asked a simple question: what's the maximum percentage a retiree could withdraw in year one — adjusted for inflation each year after — without running out of money in any historical period?

His answer was approximately 4%. A retiree with a £500,000 portfolio could withdraw £20,000 in the first year, increase that amount by inflation each year, and historically would never have gone broke over 30 years.

The "4% rule" was born. And it's been repeated in almost every retirement planning article since.

Why It Doesn't Translate to the UK

The 4% rule wasn't designed for UK retirees. It was built on US market data — specifically, the S&P 500 and US intermediate-term government bonds. The US equity market has been, by a significant margin, the best-performing major stock market of the 20th century.

This matters more than most people realise.

US exceptionalism

Research by Dimson, Marsh, and Staunton at the London Business School — who compiled the most comprehensive long-run international returns dataset available — shows that US equities returned around 6.4% per year in real terms between 1900 and 2024. UK equities returned around 5.0% over the same period.

That 1.4% annual gap compounds dramatically over a 30-year retirement. A withdrawal rate that was safe against the backdrop of US returns may not survive the lower returns that UK investors have historically experienced.

Wade Pfau extended Bengen's analysis to international markets and found that the safe withdrawal rate for many countries — including the UK — was materially lower than 4%. For some historical periods, the UK's safe rate dropped below 3.5%.

Currency and home bias

Most UK investors hold a significant portion of their portfolio in UK equities and UK bonds. The 4% rule assumes a US-dollar portfolio invested in US assets. A UK retiree holding sterling-denominated assets is exposed to a different return profile, different inflation dynamics, and different bond yields.

Even for UK investors with global equity exposure, currency fluctuations add a layer of volatility that the original 4% analysis didn't account for. A falling pound boosts the sterling value of overseas holdings — but a strengthening pound does the opposite, potentially at the worst possible time.

The Tax Problem

The 4% rule calculates a gross withdrawal rate. It says nothing about what you actually take home after tax. In the US, the tax treatment of retirement accounts (401(k), IRA, Roth IRA) is different from the UK system. Applying a US gross withdrawal rate to a UK tax situation makes little sense.

In the UK, the tax you pay on retirement withdrawals depends entirely on which accounts you draw from:

• Pension withdrawals are taxed as income. The first 25% of your pension can be taken tax-free (the tax-free lump sum), but the rest is added to your taxable income for the year.
• ISA withdrawals are completely tax-free — no Income Tax, no Capital Gains Tax, no Dividend Tax.
• GIA withdrawals may trigger Capital Gains Tax on gains and Dividend Tax on income, depending on your allowances and total income.

A 4% gross withdrawal from a pension is very different from a 4% withdrawal from an ISA. The after-tax income could vary by thousands of pounds. The 4% rule doesn't distinguish between them — it treats all money as equal, which in the UK tax system, it absolutely isn't.

The optimal strategy for most UK retirees involves blending withdrawals across account types to stay within lower tax bands. That's a fundamentally different problem from "withdraw 4% and adjust for inflation."

The State Pension Complication

The 4% rule assumes your portfolio is your only income source. But most UK retirees receive the State Pension — currently £11,973 per year for the full new State Pension.

This guaranteed, inflation-linked income changes the equation significantly. If you need £25,000 per year and the State Pension covers £12,000 of that, you only need £13,000 from your portfolio. That's a much lower withdrawal rate on your invested assets — and it means the 4% figure is irrelevant to your actual situation.

But there's a catch: the State Pension doesn't start until age 66 (rising to 67 and eventually 68). If you retire at 57, you have nearly a decade where your portfolio bears the full withdrawal burden. During those early years — when sequence-of-returns risk is highest — you may need to withdraw far more than 4%.

The 4% rule can't model this two-phase retirement. It assumes a constant withdrawal from day one. Real UK retirements don't work that way. If you want to see how the State Pension changes your withdrawal rate, you can model it for free.

The Inflation Assumption

Bengen's rule adjusts withdrawals for inflation each year. In the original analysis, this used US CPI data. UK inflation has followed a different path — and in recent years, a dramatically different one.

UK CPI hit 11.1% in October 2022. A retiree following the 4% rule would have increased their withdrawal by 11.1% that year, permanently raising their baseline for every future year. One spike in inflation ratchets up withdrawals for the rest of retirement.

The rule has no mechanism to adapt. It doesn't say "withdraw less after a market crash" or "skip the inflation increase when your portfolio is down 20%." It's a rigid formula applied to a world that doesn't behave rigidly.

What the 4% Rule Gets Right

Despite its limitations, the 4% rule did something important: it introduced the idea that withdrawal rates matter, that you can't simply spend whatever your portfolio earns, and that sequence of returns is a real risk.

Before Bengen's work, most retirement advice was vague — "save as much as you can and hope for the best." The 4% rule gave people a starting framework. It shifted the conversation from accumulation to sustainability.

That contribution shouldn't be dismissed. But a framework from 1994, built on US data, for a US tax system, assuming a single income source and a fixed 30-year horizon, has clear limits when applied to a UK retirement in 2026.

What Works Better

The honest answer is that there is no single safe withdrawal rate. The right number depends on your portfolio size, your asset allocation, your tax position, your State Pension entitlement, your spending needs, your retirement age, and the market conditions you happen to retire into.

That's not a satisfying answer — but it's an accurate one. And it's why tools that model your specific situation across thousands of possible futures are more useful than a single rule of thumb.

A Monte Carlo simulation doesn't give you one number. It gives you a probability — and it accounts for the variables that the 4% rule ignores: tax, account types, guaranteed income, variable inflation, and the sequence of returns you'll actually experience.

The 4% rule was a starting point. It was never meant to be the final answer. If you want to find a withdrawal rate that actually works for your situation, you can build a free plan and test it across 1,000 simulated futures.

Further Reading

• Bengen, W. (1994). "Determining Withdrawal Rates Using Historical Data." Journal of Financial Planning, 7(4), 171–180.
• Pfau, W. (2010). "An International Perspective on Safe Withdrawal Rates: The Demise of the 4 Percent Rule?" Journal of Financial Planning, 23(12), 52–61.
• Dimson, E., Marsh, P. & Staunton, M. (2002). Triumph of the Optimists: 101 Years of Global Investment Returns. Princeton University Press.
• Dimson, E., Marsh, P. & Staunton, M. (2024). Global Investment Returns Yearbook. UBS.