Savings & Investment Calculator
Work out how a savings account, Cash ISA or investment fund grows over time. See the power of compound interest on your monthly contributions. Free and instant.
Enter the savings details
The power of compound interest
Compound interest means you earn interest on your interest, not just on the money you put in. Over long periods this snowballs: the earlier you start and the longer you leave it, the more of your final balance comes from growth rather than your own contributions.
The calculator adds your monthly contribution each month and compounds the return, then shows the final balance and how much of it is interest or investment growth.
Savings account or investment?
A savings account or Cash ISA pays a set interest rate (AER) with no risk to your capital – ideal for an emergency fund or a short-term goal. Investing in a stocks and shares ISA or fund aims for a higher return over the long term, but the value can fall as well as rise.
As a rule of thumb, cash suits goals within about five years; investing suits longer horizons where you can ride out the ups and downs.
Tax on savings and investments
Interest on ordinary savings is covered by your Personal Savings Allowance (£1,000 for basic-rate taxpayers, £500 for higher-rate). An ISA – Cash or Stocks & Shares – shelters interest, dividends and gains from tax entirely, up to the annual ISA allowance. Enter a tax rate in the calculator to see the effect on returns held outside an ISA.
Frequently asked questions – Savings & Investment Calculator
It depends on the rate, how long you save and how often you add money. Because interest compounds, small regular contributions grow into a large sum over decades – try different monthly amounts and terms in the calculator to see the difference the time horizon makes.
AER (Annual Equivalent Rate) shows the interest you'd earn in a year including compounding, so you can compare accounts fairly. A higher AER is better; the calculator uses the annual rate you enter and compounds it for you.
A Cash ISA is a savings account with tax-free interest and no risk to your capital. A Stocks & Shares ISA invests your money for potentially higher long-term returns, but the value can go down. Cash suits short-term goals; investing suits longer ones.
Interest above your Personal Savings Allowance is taxable at your income tax rate. Money held in an ISA is free of tax on interest, dividends and gains. Enter a tax rate in the calculator to see the after-tax result on non-ISA savings.