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See what your savings could grow into with a starting amount, regular monthly top-ups and compound interest. All figures are illustrative and assume the rate stays the same throughout.
| Year | Contributed | Interest | Balance |
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For illustration only. Real-world rates can change, tax may apply outside an ISA or starting savings allowance, and providers may compound differently.
The interest a savings account pays you is not a one-off bonus at the end of the year. Most UK banks calculate interest daily and pay it monthly. Once paid, that interest sits in the same pot and earns its own interest the next day. That snowball — interest on interest — is "compounding".
The number that matters is the AER (Annual Equivalent Rate). It's the legally-required, like-for-like figure that lets you compare two accounts even if one compounds monthly and another quarterly. This calculator takes whatever AER you enter and works backwards to the periodic rate, so the answer matches what would actually land in your account.
For the first few years, regular contributions do most of the heavy lifting. Interest looks small. It's tempting to give up. But compounding is exponential, not linear: the same percentage applied to a bigger balance gives you a much bigger amount in pounds. By year ten, the interest each month often outgrows what you're contributing.
Three things mostly: rates change, tax appears, and life happens. Easy-access savings rates move with the Bank of England's base rate, so a 4.5% account today might be 3% next year. Outside an ISA, your interest counts toward the Personal Savings Allowance — basic-rate taxpayers get £1,000/year tax-free, higher-rate £500, additional-rate £0. And the average saver dips in for an unexpected boiler at least once.
No. It shows the gross figure your provider would pay. If your savings are inside a Cash ISA, the gross figure is also what you keep. Outside an ISA, deduct the tax that applies above your Personal Savings Allowance.
Because we adjust the periodic rate so the AER stays the same. Daily, monthly and yearly compounding will land within pennies of each other for the same AER over short horizons.
Yes — set the monthly contribution to £0 and the calculator becomes a pure compound interest calculator on your starting amount.