SIPP Calculator United Kingdom

In a Self-Invested Personal Pension, or SIPP, you choose the investments, the pot grows free of Income Tax and Capital Gains Tax, and the government adds tax relief to every contribution. This calculator projects how your pot could grow. It takes your current balance and monthly net contribution, adds the 20% basic rate relief that HMRC pays into the pension at source, and compounds the total each month at the return you expect.

How tax relief boosts your contributions

When you pay a net amount into a SIPP, your provider claims basic rate Income Tax from HMRC and adds it to your pot. With 20% relief, a net contribution is divided by 0.8 to find the amount invested: an £80 net payment becomes £100 in the pension, and a £200 monthly net contribution becomes £250. Over decades this uplift compounds alongside your own money, so the relief figure in the results is often larger than people expect. The calculator reads the basic rate from a stored parameter, so the projection follows any change in the rate.

How the projection compounds

The tool divides your expected annual return by twelve for a monthly rate and multiplies the years by twelve for the number of months. Your starting pot grows at that monthly rate for the whole term, and each grossed-up monthly contribution grows for the time left after it is paid in. The two together give the projected pot. At a zero return the result is the starting pot plus total gross contributions: £1,000 gross a month for a year with no growth gives exactly £12,000.

The return you enter is nominal, not adjusted for inflation, so a large pot decades from now will buy less than the same figure today. For a result in today’s money, enter a real return: your expected growth minus inflation. The projection is far more sensitive to the length of the term and the return than to any single month’s contribution.

Reading the three results

The projected pot is the total value at the end of the term. Total net contributions is the cash that left your bank account: your starting pot plus every net monthly payment. Basic rate tax relief added is what HMRC paid into the pension for you. The donut chart splits the projected pot into net contributions, tax relief and investment growth, which add up to the total.

A worked example

Suppose you hold £20,000 in a SIPP and pay in £200 net a month, expecting a 5% annual return over 25 years. Each £200 is grossed up to £250, so £3,000 of gross contributions goes in each year. After 25 years the projected pot is about £218,503. Of that, £80,000 is your own money, £15,000 is basic rate relief from HMRC, and the remaining £123,500 or so is investment growth on the combined balance.

Common mistakes to avoid

• Entering the gross contribution in the net field, which counts the relief twice. Enter what leaves your bank account and let the tool add the 20%.
• Assuming a high return every year. Markets are volatile, and a smooth projection can flatter a pot that suffers falls along the way, so test a range.
• Ignoring charges. A 1% annual fee on a large pot is a substantial sum over decades, so subtract expected fees from the return you enter.
• Expecting higher rate relief in the pot. The extra relief you reclaim through Self Assessment is not added here.

How to read your result

Look at the growth slice on the donut as well as the total: in a long projection, compounding should be doing much of the work, which is the reward for starting early and staying invested. Use the tool for practical questions, such as how much a £50 increase to your monthly payment adds by retirement or what five extra years change. Because it ignores the annual allowance and your earnings, check that your planned contributions qualify for relief before relying on the projection.

Assumptions and limitations

This is a planning estimate, not advice or a guarantee. It assumes a constant annual return with monthly compounding and that every contribution qualifies for basic rate relief at source. It does not check your payments against the annual allowance or your earnings, does not model the extra relief higher and additional rate taxpayers can reclaim, and ignores provider and fund charges. Investment values can fall as well as rise, so treat the return as an assumption to test. For decisions about your own retirement, check the current gov.uk guidance or speak to a regulated financial adviser.

About This SIPP Calculator

Use this SIPP calculator to get an instant, accurate estimate. The figures follow official GOV.UK guidance and every rate and threshold is kept up to date for 2026. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.