Calculate how compound interest can grow your savings or investments over time. Include regular deposits, withdrawals and inflation adjustments, with monthly or yearly breakdowns.
| Month | Deposits & withdrawals | Interest | Total deposits & withdrawals | Accrued interest | Balance |
|---|---|---|---|---|---|
| 0 | £5,000.00 | – | £5,000.00 | – | £5,000.00 |
| 1 | – | £20.83 | £5,000.00 | £20.83 | £5,020.83 |
| 2 | – | £20.92 | £5,000.00 | £41.75 | £5,041.75 |
| 3 | – | £21.01 | £5,000.00 | £62.76 | £5,062.76 |
| 4 | – | £21.09 | £5,000.00 | £83.86 | £5,083.86 |
| 5 | – | £21.18 | £5,000.00 | £105.04 | £5,105.04 |
| 6 | – | £21.27 | £5,000.00 | £126.31 | £5,126.31 |
| 7 | – | £21.36 | £5,000.00 | £147.67 | £5,147.67 |
| 8 | – | £21.45 | £5,000.00 | £169.12 | £5,169.12 |
| 9 | – | £21.54 | £5,000.00 | £190.66 | £5,190.66 |
| 10 | – | £21.63 | £5,000.00 | £212.28 | £5,212.28 |
| 11 | – | £21.72 | £5,000.00 | £234.00 | £5,234.00 |
| 12 | – | £21.81 | £5,000.00 | £255.81 | £5,255.81 |
| 13 | – | £21.90 | £5,000.00 | £277.71 | £5,277.71 |
| 14 | – | £21.99 | £5,000.00 | £299.70 | £5,299.70 |
| 15 | – | £22.08 | £5,000.00 | £321.78 | £5,321.78 |
| 16 | – | £22.17 | £5,000.00 | £343.96 | £5,343.96 |
| 17 | – | £22.27 | £5,000.00 | £366.22 | £5,366.22 |
| 18 | – | £22.36 | £5,000.00 | £388.58 | £5,388.58 |
| 19 | – | £22.45 | £5,000.00 | £411.03 | £5,411.03 |
| 20 | – | £22.55 | £5,000.00 | £433.58 | £5,433.58 |
| 21 | – | £22.64 | £5,000.00 | £456.22 | £5,456.22 |
| 22 | – | £22.73 | £5,000.00 | £478.95 | £5,478.95 |
| 23 | – | £22.83 | £5,000.00 | £501.78 | £5,501.78 |
| 24 | – | £22.92 | £5,000.00 | £524.71 | £5,524.71 |
| 25 | – | £23.02 | £5,000.00 | £547.73 | £5,547.73 |
| 26 | – | £23.12 | £5,000.00 | £570.84 | £5,570.84 |
| 27 | – | £23.21 | £5,000.00 | £594.05 | £5,594.05 |
| 28 | – | £23.31 | £5,000.00 | £617.36 | £5,617.36 |
| 29 | – | £23.41 | £5,000.00 | £640.77 | £5,640.77 |
| 30 | – | £23.50 | £5,000.00 | £664.27 | £5,664.27 |
| 31 | – | £23.60 | £5,000.00 | £687.87 | £5,687.87 |
| 32 | – | £23.70 | £5,000.00 | £711.57 | £5,711.57 |
| 33 | – | £23.80 | £5,000.00 | £735.37 | £5,735.37 |
| 34 | – | £23.90 | £5,000.00 | £759.27 | £5,759.27 |
| 35 | – | £24.00 | £5,000.00 | £783.26 | £5,783.26 |
| 36 | – | £24.10 | £5,000.00 | £807.36 | £5,807.36 |
| 37 | – | £24.20 | £5,000.00 | £831.56 | £5,831.56 |
| 38 | – | £24.30 | £5,000.00 | £855.86 | £5,855.86 |
| 39 | – | £24.40 | £5,000.00 | £880.26 | £5,880.26 |
| 40 | – | £24.50 | £5,000.00 | £904.76 | £5,904.76 |
| 41 | – | £24.60 | £5,000.00 | £929.36 | £5,929.36 |
| 42 | – | £24.71 | £5,000.00 | £954.07 | £5,954.07 |
| 43 | – | £24.81 | £5,000.00 | £978.87 | £5,978.87 |
| 44 | – | £24.91 | £5,000.00 | £1,003.79 | £6,003.79 |
| 45 | – | £25.02 | £5,000.00 | £1,028.80 | £6,028.80 |
| 46 | – | £25.12 | £5,000.00 | £1,053.92 | £6,053.92 |
| 47 | – | £25.22 | £5,000.00 | £1,079.15 | £6,079.15 |
| 48 | – | £25.33 | £5,000.00 | £1,104.48 | £6,104.48 |
| 49 | – | £25.44 | £5,000.00 | £1,129.91 | £6,129.91 |
| 50 | – | £25.54 | £5,000.00 | £1,155.45 | £6,155.45 |
| 51 | – | £25.65 | £5,000.00 | £1,181.10 | £6,181.10 |
| 52 | – | £25.75 | £5,000.00 | £1,206.86 | £6,206.86 |
| 53 | – | £25.86 | £5,000.00 | £1,232.72 | £6,232.72 |
| 54 | – | £25.97 | £5,000.00 | £1,258.69 | £6,258.69 |
| 55 | – | £26.08 | £5,000.00 | £1,284.77 | £6,284.77 |
| 56 | – | £26.19 | £5,000.00 | £1,310.95 | £6,310.95 |
| 57 | – | £26.30 | £5,000.00 | £1,337.25 | £6,337.25 |
| 58 | – | £26.41 | £5,000.00 | £1,363.65 | £6,363.65 |
| 59 | – | £26.52 | £5,000.00 | £1,390.17 | £6,390.17 |
| 60 | – | £26.63 | £5,000.00 | £1,416.79 | £6,416.79 |
Estimate pension tax relief, ISA allowance usage and tax on pension withdrawals. Rates are set for England, Wales and Northern Ireland, 2026/27.
Simplified illustration. It excludes Scottish Income Tax, National Insurance, employer contributions, carry forward, tapered annual allowance detail, Marriage Allowance, savings/dividend income and provider charges. Pension access can trigger the Money Purchase Annual Allowance.
Short, practical explainers designed to accompany the calculators. These examples are educational rather than recommendations.
Compound interest means returns are earned on the original capital and on earlier returns. Over long periods, the combination of time, return and regular contributions can matter more than any single year's performance.
Compare a lump sum with the same lump sum plus monthly deposits using the calculator above. Try several return assumptions rather than relying on one forecast.
For a lump sum, the core formula is A = P(1 + r/n)nt, where P is principal, r is the annual rate, n is compounding periods per year and t is years. Regular cash flows require each deposit or withdrawal to be compounded for the time it remains invested.
A SIPP is a registered pension. Pension contributions can receive tax relief, but personal relief and the pension Annual Allowance are separate tests. The standard Annual Allowance is currently £60,000, while high income or flexible pension access can reduce it.
An ISA generally offers tax-free growth and withdrawals, while a SIPP generally gives pension tax relief on contributions but normally restricts access until pension age and can create taxable income when benefits are drawn. The better mix depends on access needs and tax position.
Pension withdrawals can contain tax-free and taxable elements. Use the retirement-income field to see how a taxable SIPP withdrawal can sit on top of other pension income. Actual treatment varies by withdrawal method and individual circumstances.
A positive investment return does not necessarily mean purchasing power rises by the same amount. For scenario testing, compare nominal growth with a lower real-return assumption after allowing for inflation and charges.
Start with desired annual spending, then subtract secure income such as defined-benefit and State Pension income. The remaining spending gap can be modelled as withdrawals from a SIPP or ISA while varying return, inflation and term.
Try 3%, 5% and 7% annual returns, then vary contributions and withdrawals. A range of assumptions gives a more useful planning picture than presenting a single growth rate as an expected outcome.
Compound growth: the calculator applies the selected annual rate at the chosen compounding frequency. Regular deposits or withdrawals are then incorporated across the selected term.
SIPP: the tax estimate models pension contribution relief against taxable income. Relief can depend on earnings, contribution method, annual allowance, tapering, carry forward and whether flexible pension access has triggered the MPAA.
ISA: ISA growth and withdrawals are modelled tax-free. The allowance check uses the selected tax year's overall ISA limit.
This calculator is designed to help people explore long-term saving, investing and retirement scenarios in one place. Change the assumptions to compare possible outcomes rather than treating any single projection as a forecast.
The site is independent and is not a bank, investment provider, pension provider or financial adviser.
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Results are estimates for educational and planning purposes only and are not financial, tax, legal or investment advice. Investment values can fall as well as rise. Tax treatment depends on individual circumstances and rules can change.
Before making significant pension, investment or tax decisions, check current HMRC guidance and consider regulated professional advice where appropriate.
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For illustrative purposes only. Results are estimates and do not constitute financial advice. Actual investment returns may vary and can be negative.