How this calculator works

This planner projects every part of your retirement wealth separately, workplace and personal pensions, ISAs, general investment accounts, cash savings, and property, then adds them together to see whether you're on track for the retirement income you've told it you want.

Each pot grows using compound monthly growth at the rate you specify, minus any platform charge, over the number of years between your current age and your chosen retirement age. Pensions let you add employee and employer contributions separately, since employer contributions are effectively free money on top of your own.

Cash savings work slightly differently to the other buckets, because unlike a pension or ISA wrapper, interest earned outside an ISA is taxable once it exceeds your Personal Savings Allowance. If you mark your cash as not held in an ISA, the calculator applies that tax automatically each year at your selected Income Tax band, the same mechanic used on our savings calculator.

Your required pot is worked out by taking your target annual income, inflating it forward to the value it'll need to be in the year you retire, subtracting any guaranteed income from the State Pension and a defined benefit pension if you have one, then dividing what's left by your chosen withdrawal rate. The 4% rate offered as the default comes from the Trinity Study, a widely cited piece of research into how much a retirement pot can sustainably support each year without running out.

One interaction worth understanding: the State Pension only counts if your retirement age is at or above State Pension age, currently 67. If you set a retirement age below that, and plenty of people do, the calculator correctly excludes State Pension income entirely for those years, even with "Include State Pension" switched on, because you genuinely wouldn't receive it yet. This is the single most common source of an unexpectedly large shortfall in the results.

Understanding your inputs

Current Age and Retirement Age set the number of years every projection runs for.

Pensions can be added individually, useful if you've built up pots with more than one employer. Mark old workplace pensions you're no longer contributing to as Frozen rather than Active, they still grow, just without new contributions.

Target Annual Income is in today's money, the calculator inflates it forward for you, so you don't need to guess a future figure yourself.

Include State Pension and Defined Benefit Pension represent guaranteed income that reduces how much your own pot needs to provide. Only include a DB pension figure if you actually have one, most people with only workplace and personal pensions don't.

Property is shown separately from your liquid wealth throughout, because unlike a pension or ISA, you generally can't spend it without selling or downsizing.

Worked example

Take this calculator's own defaults: age 35 now, retiring at 65, a single workplace pension worth £25,000 growing at 5% with combined contributions of £450 a month, an ISA with £200 a month growing at 7%, £5,000 in ordinary (non-ISA) cash savings, a target income of £30,000 a year, and the standard 4% withdrawal rate.

By 65, that pension alone grows to roughly £409,000, the ISA to around £223,000, and the cash pot, after Personal Savings Allowance tax at the basic rate, to about £18,700, a liquid pot of roughly £651,000. The target income of £30,000 inflates to about £62,900 a year in 30 years' time. Because 65 is below State Pension age, none of that guaranteed income counts here, so the full inflated target has to come from the pot, requiring roughly £1,573,000 at a 4% withdrawal rate. That leaves a shortfall of around £922,000, needing an extra £917.85 a month in additional contributions from now to close it entirely, or a combination of working longer, saving more, or accepting a lower target income.

Push retirement age out to 67 instead, and the picture changes substantially, State Pension alone contributes close to £27,650 a year by then, cutting the amount the pot itself needs to provide by nearly half.

2026/27 figures used in this planner

Common Mistakes

The most common one, by far, is missing the State Pension age interaction described above. Setting a retirement age below 67 with State Pension switched on can produce a shortfall that looks alarming but is partly an artefact of retiring before that guaranteed income actually starts, not purely a savings problem.

Another is leaving old pensions out entirely because they feel disconnected from your current job. A frozen pension from three employers ago still counts toward your total wealth and still grows, add every pot you have, not just the one you're actively paying into.

People also frequently enter their target income as a gross figure without thinking about tax on withdrawal. Pension drawdown income is generally taxable, so if £30,000 a year is what you actually want in your pocket, you may need to target a higher gross figure, this calculator takes your number as stated, it doesn't add tax on top automatically.

Finally, treating the 4% withdrawal rate as a guarantee rather than a rule of thumb is a real risk. It's a well-researched starting point, not a promise, market conditions in the specific years around your retirement can meaningfully affect how sustainable any withdrawal rate turns out to be in practice.

Sources and verification

Figures verified against HMRC, DWP and GOV.UK on 03 September 2026. Applies to the 2026/27 tax year.

State Pension amount and age: DWP/House of Commons Library. Pension Annual Allowance: HMRC. ISA allowance: GOV.UK. Personal Savings Allowance: HMRC. The 4% withdrawal rate default references the Trinity Study, an independent academic analysis of sustainable withdrawal rates, not a government or regulatory figure.