Set your pot, the income you want, and a return. See the exact age your money could run out, or whether it lasts a lifetime.
Each year your remaining pot earns its return, then you take out the income you need; whatever is left grows again the next year. Your money lasts until the pot hits zero. The withdrawal rate, the income you take divided by your pot, is the single biggest factor: a small rate can last forever, a large one drains fast.
Example: a £500,000 pot earning 3% a year after inflation. Draw £20,000 (4%) and it lasts well over 40 years, effectively a lifetime. Draw £30,000 (6%) and it runs dry in about 24 years; draw £40,000 (8%) and it is gone in roughly 16. Same pot, same returns, the only difference is the speed you spend it.
The State Pension changes everything. If you want £30,000 a year and the State Pension pays ~£12,500, you only draw ~£17,500 from the pot (3.5%) instead of the full £30,000 (6%), turning a 24-year pot into one that can last a lifetime.
This models a steady real return; real markets rise and fall, and a poor run early in retirement (sequence-of-returns risk) does more damage than the same fall later, which is why a 4% start is built with a safety margin. The State Pension is assumed to run alongside your drawdown from your retirement date; in reality it starts at State Pension age (currently 66, rising to 67). Returns are not guaranteed and your capital is at risk.
Illustrative only, not financial advice. This models a constant annual return after inflation and a steady inflation-linked income; real returns vary year to year, and fees, tax, your actual life expectancy and the timing of market falls all affect the outcome. Your capital is at risk, investments can fall as well as rise. Figures use the 2026/27 tax year. Always do your own research or speak to a qualified adviser.
See also the retirement number calculator and the compound growth calculator.