Your retirement number: understanding safe withdrawal rates

Retirement is a cash-flow question

A retirement plan begins with the life you want to fund. Estimate annual spending, subtract reliable income such as defined-benefit pensions or a State Pension, and the remainder is the amount your portfolio may need to support.

A safe withdrawal rate is the percentage of a starting portfolio withdrawn in year one, with later withdrawals usually increased for inflation in the classic research. It is a planning convention rather than a promise that money will last.

Why the 4% rule became famous

Research commonly known as the Trinity Study tested stock-and-bond portfolios across historical US market periods. A 4% starting withdrawal rate became a widely used rule of thumb for a 30-year retirement. Turning the percentage around gives the ‘rule of 25’: annual portfolio spending multiplied by 25.

If a household expects to draw £30,000 a year from investments, 4% implies a £750,000 starting portfolio. A 3.5% assumption implies about £857,000. A lower rate demands a larger pot because each pound of capital is expected to support less annual spending.

The rule has boundaries

The original evidence used US returns and historical sequences. A UK investor may face different market exposure, fees, taxes and inflation. Retiring early extends the horizon, while poor returns early in retirement can have an outsized effect when withdrawals continue through a falling market.

Flexible spending, a cash reserve, later earned income, annuity income and a diversified portfolio can change the result. A useful plan examines several withdrawal rates and revisits them as circumstances evolve.

Bring other retirement income into the picture

The full new State Pension is £241.30 a week in the 2026/27 tax year, although the amount each person receives depends on their National Insurance record. That is about £12,548 a year before tax for someone entitled to the full rate.

If annual retirement spending is £30,000 and £12,548 is covered by the State Pension, the portfolio gap becomes roughly £17,452. At a 3.5% withdrawal rate, that points to a portfolio near £499,000 once the pension begins. Someone retiring earlier also needs a bridge for the years before pension income starts.

Check your own State Pension forecast and pension age. Workplace pensions, defined-benefit income, tax and household circumstances deserve their own lines in the plan.