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Compound interest calculator

Final value, contributions, growth, and a year-by-year chart.

Calculated in this page. Nothing you type is sent to a server.

These figures are estimates. They are not tax advice and they are not financial advice.

Final value£39,291.54
Total contributed£24,000.00
Total growth£10,291.54

Each month, that month’s interest is added and then any contribution due. Monthly compounding uses the annual rate divided by 12. A monthly contribution is added after that month’s interest. A yearly increase starts in year 2 and compounds. Growth is the final value minus the starting amount minus everything contributed. Leave inflation blank and the real value is not shown.

Value at the end of each yearStartYear 10
Year-by-year
Opening value, contributions, growth and closing value for each year.
YearOpeningContributedGrowthClosing
1£5,000.00£2,400.00£311.58£7,711.58
2£7,711.58£2,400.00£450.32£10,561.90
3£10,561.90£2,400.00£596.13£13,558.03
4£13,558.03£2,400.00£749.42£16,707.45
5£16,707.45£2,400.00£910.57£20,018.02
6£20,018.02£2,400.00£1,079.94£23,497.96
7£23,497.96£2,400.00£1,257.98£27,155.94
8£27,155.94£2,400.00£1,445.12£31,001.06
9£31,001.06£2,400.00£1,641.84£35,042.90
10£35,042.90£2,400.00£1,848.64£39,291.54

An ISA shelters interest and investment growth from tax. In 2026/27 the most you can put into ISAs is £20,000.00. Outside an ISA, the Personal Savings Allowance is £1,000.00 for a basic-rate taxpayer, £500.00 for a higher-rate taxpayer, and £0.00 for an additional-rate taxpayer. If your other taxable income is under £17,570.00, a starting rate for savings of up to £5,000.00 can also apply, and it tapers as that other income rises. This page does not deduct tax. Individual Savings Accounts · Tax-free interest · Capital gains on shares and funds

How to use it

  1. Enter the starting amount, the contribution, the annual rate and the number of years.
  2. Choose monthly or annual contributions, or none, and annual, monthly or daily compounding.
  3. Add a yearly contribution increase or an inflation rate if you want a real value.
  4. Read the final value, what you put in, and the growth. Open the year-by-year table for the path.

What happens in a month

These figures are estimates. They are not tax advice and they are not financial advice. Each month, that month’s interest is added and then any contribution due. Monthly compounding uses the annual rate divided by 12. Daily compounding uses a 365-day year and the lengths of a non-leap year. Annual compounding is added once, in December, before that month’s contribution. A contribution increase starts in year 2.

£1,000 at 5% compounded once is £1,050. £1,000 plus £100 a month, with no interest, is £2,200 after a year, of which £1,200 was contributed. Growth is the final value minus the start minus everything contributed, so those two identities hold. Interest is rounded to the nearest penny each time it is added.

The figure is before tax

An ISA shelters interest and investment growth from tax. In 2026/27 you can put up to £20,000 into ISAs. Outside an ISA, the Personal Savings Allowance is £1,000 for a basic-rate taxpayer, £500 for a higher-rate taxpayer and nothing for an additional-rate taxpayer. A starting rate for savings of up to £5,000 can apply when other taxable income is under £17,570, and it tapers. This page does not work out that tax. A gain on shares outside an ISA is a different calculation: use the capital gains tax calculator.

Questions

Does the real value predict inflation?

No. It divides each year’s closing value by (1 + the inflation rate you typed) to the power of the year. It shows purchasing power at that assumed rate.

Why can daily and monthly results differ?

Daily compounding applies the rate over the days in each month of a non-leap year. Monthly compounding uses one twelfth of the annual rate. Neither is an APR conversion.

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