See what your savings grow to when interest earns interest, with or without regular deposits.
Final balance
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Enter a starting amount and a rate to see the result.
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| Year | Paid in so far | Interest that year | Balance at year end |
|---|---|---|---|
The year-by-year table appears with the result.
| Calculation | Date | Actions |
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Nothing yet: copy, export or save a calculation to find it here.
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Enter what you start with, the annual interest rate, how often interest is added and the term, then any regular deposit. The calculator shows the final balance, what you paid in, the interest earned and the AER, with every step of the working and a year-by-year table. It assumes the rate stays the same for the whole term and works before tax, fees and withdrawals. The arithmetic is the same in England, Scotland, Wales and Northern Ireland.
The starting amount is what you put in on day one; enter 0 if you start from nothing. The rate is the yearly rate before tax. The term is a whole number of years, from 1 to 60.
At the same rate, interest added more often earns more, because the interest itself starts earning interest sooner. An AER (annual equivalent rate) shows what the rate would be if interest were added once a year, so it already includes this effect: if you only know the AER, choose Yearly. If you know the gross rate and how often interest is added to the account, enter both.
A monthly or yearly deposit is added on the last day of each month or year if you pay in at the end of each period, or on the first day if you pay in at the start, when it earns interest for that period too. A deposit made between two interest dates earns simple interest until the next one, then compounds, as in an account that adds interest once a year.
The final balance splits into what you paid in and the interest earned. The starting amount and the deposits are each valued to the nearest penny (half a penny rounds up), then added. The year-by-year table shows each year's interest growing: that is compounding at work. You can copy the result, export it as CSV or save it to Priostack.
Starting amount at the end = amount × (1 + rate ÷ n)^(n × years), where n is how many times a year interest is added: 1, 4, 12 or 365.
Deposits made on the interest dates: deposit × ((1 + rate ÷ n)^(n × years) − 1) ÷ (rate ÷ n), times (1 + rate ÷ n) if they are made at the start of each period.
Monthly deposits with interest added once a year: each year of deposits is worth deposit × (12 + rate × 66 ÷ 12) on the interest date, 66 being the months of simple interest (11 + 10 + … + 0); 78 for deposits at the start of each month.
AER = (1 + rate ÷ n)^n − 1.
With interest added monthly and £200 paid in at the end of each month, the £10,000 grows to £10,000.00 × (1 + 4% ÷ 12)^120 = £14,908.33, and the 120 deposits are worth £29,449.96. The final balance is £44,358.29 for £34,000.00 paid in, so £10,358.29 of interest. A 4% rate added monthly is an AER of 4.074%.
With simple interest only the original £1,000 earns: at 5% a year that is £50 a year, or £1,500 after 10 years. With compound interest added yearly, each year's interest earns too: £1,000 × 1.05^10 = £1,628.89, which is £128.89 more. The gap widens with the rate and the term.
NS&I describes the AER as what the annual rate would be if interest were compounded each time it was paid; where interest is paid once a year, the quoted rate and the AER are the same. NS&I Income Bonds, for example, quote 3.69% gross, paid monthly, as 3.75% AER. If the interest stays in the account, enter the gross rate with how often it is added, or the AER with Yearly. For a lump sum the two give the same balance, to within the rounding of the AER. With regular deposits they differ slightly, because with Yearly a deposit earns simple interest until the next interest date: £100 paid in at the end of each month for a year grows to £1,220.50 at 3.69% added monthly and to £1,220.63 at 3.75% added yearly.
Your provider may credit interest in whole pennies each time it adds it and work out the next payment on that rounded balance; the calculator rounds once, at the end. NS&I's own figures show such a gap: it shows £1,000 in its 5-year Guaranteed Growth Bond at 5.17% gross/AER growing to £1,286.64, while £1,000 × 1.0517^5 = £1,286.6469, which rounds to £1,286.65.
The calculator works before tax. You do not usually pay tax on interest in an ISA. Outside one, the Personal Savings Allowance lets you earn £1,000 of interest in a tax year without tax as a basic-rate taxpayer, £500 as a higher-rate taxpayer and nothing as an additional-rate taxpayer, and the starting rate for savings can add up to £5,000 if your other taxable income is below £17,570. In Scotland you pay the same tax on savings interest as the rest of the UK. The tax year runs from 6 April to 5 April.
A little: a deposit at the start of the month earns one more month of interest. £100 a month for a year at 4%, with interest added once a year, grows to £1,222.00 when paid at the end of each month and £1,226.00 when paid at the start.
Only as a rough guide. It assumes a fixed rate added at regular dates, with no fees, tax or withdrawals. For an investment whose value goes up and down, the rate you enter is an assumption, not a promise.
This calculator gives general information. It is not legal, tax, financial or accounting advice. It assumes a fixed rate with no fees, tax or withdrawals: check the terms of your account with your provider.
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