UK Pension Drawdown Calculator

What is the biggest hidden risk when you start drawing a pension?

The biggest hidden risk is sequence-of-returns risk: poor returns in your first years of drawdown can permanently shrink a pot that averages said was safe. This is the decumulation phase — the switch from growing your wealth to spending it — and its danger is barely mentioned in most personal finance content.

You've spent 20 or 30 years building your pot, invested regularly, and stayed the course through crashes. (If you want to see how that pot was built — what a lump sum in the S&P 500 would have grown to — the S&P 500 Calculator models the accumulation side.) The one question that now matters is whether it lasts as long as you need — and that depends less on the average return than on the order the returns arrive in.

What is sequence-of-returns risk?

Sequence-of-returns risk is the danger that poor early returns, combined with withdrawals, permanently damage your pot even if your average return is fine. Imagine two investors who both retire with £500,000, withdraw £25,000 a year, and average 6% over 25 years — but one gets the bad years first. That investor can be wiped out while the other thrives.

Why? Withdrawing during a downturn forces you to sell shares at low prices, and those shares can't share in the recovery. As markets rebound your pot has fewer assets to appreciate, and each withdrawal then takes an ever-larger slice of what remains.

What does the 4% rule actually say?

The 4% rule says a 4% initial withdrawal, rising yearly with inflation, historically survived most 30-year US retirements; UK research leans to 3–3.5%. It emerged from the Trinity Study, which analysed US stock and bond portfolios from 1926 onwards.

It's a useful starting point, with important caveats:

• It was based on US data. UK and global portfolios may behave somewhat differently.
• It assumed a balanced portfolio — roughly 50–75% equities.
• The study's definition of "success" simply meant the portfolio didn't hit zero.
• Longer retirements — 35 or 40 years — substantially increase depletion risk.
• Fees, taxes, and behavioural decisions are not factored in.

How do you read the simulator results?

Each grey line is one real historical retirement; the coloured lines mark the best, worst, typical and percentile outcomes — the full range, not an average. The chart plots every historical drawdown window; overlaid on top are seven reference lines:

• Absolute best (bright green, solid) — the single best retirement start date in the entire dataset.
• Absolute worst (bright red, solid) — the single worst retirement start date.
• Typical outcome (white) — the median result. Half of all historical retirees did better, half did worse.
• Good era (orange, dashed) — better than 75% of all historical starts.
• Tough era (purple, dashed) — worse than 75% of all historical starts.
• Best 10% (teal, dashed) — the 90th percentile.
• Worst 10% (amber, dashed) — the 10th percentile.

How should you use these results practically?

Use the range, not one number: find the withdrawal rate that keeps your historical survival rate above 90%, and plan for the worst case, not the average. The worst S&P 500 scenario is typically a retirement starting in the late 1960s, as stagflation eroded returns and purchasing power for over a decade; the best outcomes cluster around retirements that began just after major crashes.

Neither extreme is a prediction, but the range they define is the most honest answer history can give about what's possible. Pair this with the rolling returns simulator to see how the same market history treats the saving-up phase.

What can you do if the numbers look worrying?

Three levers improve survival the most — flexible withdrawals, a cash buffer, and protecting the first five years:

• Use flexible withdrawals. Reducing withdrawals by 10–20% during a prolonged downturn can dramatically improve survival rates.
• Keep a cash buffer. Holding 1–2 years of living expenses in cash means you never have to sell equities during a downturn.
• Protect the critical first five years. The first five years of retirement are the most dangerous from a sequence-of-returns perspective.

How does the State Pension change how much you need?

The full new State Pension pays £12,548 a year in 2026/27 (£241.30 a week), which can cover essential spending and let your pot draw a lower, safer rate. That guaranteed, inflation-linked income behaves like an annuity you already own, so many retirees only need their pot to fund the gap above it. If you don't need it the moment you reach State Pension age, our State Pension deferral calculator shows how delaying it lifts that guaranteed income for life.

Two rules shape the pot itself: you can normally take 25% tax-free (capped at a £268,275 lump sum allowance), and the minimum access age rises from 55 to 57 on 6 April 2028 (gov.uk, correct as of 2026-08-21). Model the pot after your tax-free lump sum here, and use the FIRE calculator if you're planning to retire early.

What data does this simulator use, and what are its limits?

It uses the S&P 500 total-return index (dividends reinvested) from March 1957, so results reflect US large-cap history, not a projection. Most UK pension and ISA portfolios hold global equity funds rather than the S&P 500 alone, so your own results may differ — though the structural lessons about sequence risk apply universally.

The simulation excludes platform fees, fund charges, tax on withdrawals and State Pension income; realistic costs would reduce the results shown by roughly 0.3–0.7% per year.