Plan a savings goal and see how it builds. Combine a starting balance with a regular monthly deposit and an interest rate, and the calculator shows what you'll have — and how much of it is interest.
Lump sum plus monthly deposits
Savings grow through two things: the money you pay in, and the interest the bank pays you. When interest is added back to your balance it starts earning interest itself — that's compounding. The longer you save and the higher the rate, the bigger the snowball.
The calculator combines a compound-interest formula on your starting balance with the future value of your monthly deposits, so the interest earned is shown separately from the cash you contributed.
Start with £5,000, add £100 a month at 4.5% for 3 years. You pay in £3,600 of deposits on top of the £5,000 start (£8,600 total), and finish with about £9,568 — roughly £968 of interest.
| Monthly deposit | Balance after 3 yrs | Interest earned |
|---|---|---|
| £50 | £7,640 | £840 |
| £100 | £9,568 | £968 |
| £200 | £13,424 | £1,224 |
| £300 | £17,280 | £1,480 |
Interest is taxable, but most people don't pay anything thanks to the Personal Savings Allowance — £1,000 for basic-rate, £500 for higher-rate, £0 for additional-rate taxpayers. Above that, interest is taxed at your income tax rate. To keep interest fully tax-free, use a Cash ISA. The compound interest calculator lets you model different compounding frequencies, and the take-home pay calculator shows what you can comfortably set aside.
Starting with £5,000 and adding £100 a month at 4.5% for 3 years grows to about £9,568. You pay in £8,600 in total and earn roughly £968 of interest.
Most accounts compound interest monthly or annually. The calculator applies A = P(1 + r/n)nt to your starting balance and adds the future value of your deposits, so you see contributions and interest separately.
You might. Basic-rate taxpayers get a £1,000 Personal Savings Allowance, higher-rate £500, additional-rate £0. Interest above your allowance is taxed at your income tax rate. Cash ISAs are always tax-free.
AER (Annual Equivalent Rate) shows the rate as if interest were paid and compounded once a year, making accounts easy to compare. The gross rate is the rate before tax and before compounding is factored in.
