Savings Growth Calculator
Project how a savings balance could grow from regular monthly deposits and compound interest.
Enter what you have saved now, what you plan to add each month and an interest rate. Figures update as you type and never leave your browser.
Your projected savings
Growth over time
Your projected balance against the total you’ve paid in. The widening gap between the two lines is interest — including interest earned on earlier interest.
Year-by-year breakdown
What goes in, what interest adds and where the balance ends up at the end of each year.
| Year | Paid in that year | Interest that year | Total paid in | Total interest | Balance at year end |
|---|
How this savings calculation works
The calculator steps through your savings one month at a time. Each month it adds interest to the balance and adds your deposit — before the interest if you choose start-of-month deposits, after it if you choose end-of-month. Interest earned stays in the account, so the following month earns interest on it too. That’s compound interest, and it’s why the gap between the two lines on the chart widens over time rather than growing in a straight line.
Turning an AER into a monthly rate
Savings rates in the UK are quoted as an AER (annual equivalent rate): the growth you’d get over a full year with interest compounded. Dividing the AER by 12 would slightly overstate growth, so the calculator uses the monthly rate that compounds back to exactly the AER: monthly rate = (1 + AER)1/12 − 1. At 4% AER that’s about 0.3274% a month, and £1,000 left untouched for a year grows to exactly £1,040.
Real accounts usually calculate interest daily and pay it monthly or annually. Because the AER is designed to make those arrangements comparable, using the AER-equivalent monthly rate gives very close results for a balance that stays in the account — but it won’t match a bank statement to the penny.
Start or end of the month?
A deposit made at the start of a month earns that month’s interest; one made at the end doesn’t start earning until the following month. Over many years the difference is noticeable but small next to the effect of the rate and how much you pay in.
What the projection assumes
- The rate never changes. Most easy-access rates are variable and can move at any time, and fixed rates only last for their term. The figures are an illustration of one rate, not a forecast.
- Deposits are the same every month and nothing is withdrawn.
- No tax is deducted. UK savings interest is paid gross. Interest within your Personal Savings Allowance — £1,000 a year for basic-rate taxpayers, £500 for higher-rate and nothing for additional-rate — is tax-free, and interest in a cash ISA is tax-free regardless. Interest above your allowance is taxable at your income tax rate.
- No inflation adjustment. The final balance is in future pounds, which may buy less than the same amount today.
- No bonus or introductory rates, fees or account limits.
If you want to work backwards from a target instead, the Savings Goal Calculator finds the monthly deposit needed to reach it.
Sources
-
GOV.UK — Tax on savings interest: how much is tax-free
The Personal Savings Allowance (£1,000 basic rate, £500 higher rate, £0 additional rate) and the starting rate for savings of up to £5,000.
Frequently asked questions
What does AER mean?
AER stands for annual equivalent rate. It shows what interest would add over a year if it were compounded, so accounts that pay interest monthly and annually can be compared fairly. This calculator converts the AER into the equivalent monthly rate rather than simply dividing by 12.
Is the interest in this projection taxed?
No. The projection shows interest before any tax. Most people can earn some interest tax-free through the Personal Savings Allowance, and cash ISA interest is tax-free, but interest above your allowance is taxed at your income tax rate. If you expect to go over your allowance, the after-tax growth will be lower than shown.
Why does the balance grow faster in later years?
Because interest is earned on the whole balance, including interest added in earlier months. The larger the balance gets, the more interest each month adds, so growth accelerates even if your deposits stay the same.
What if my savings rate changes?
The calculator assumes one rate for the whole period. If your rate is variable, try running it at a lower and a higher rate to see a range of outcomes rather than relying on one figure.
Does it take inflation into account?
No. All figures are in pounds at the time they are reached. Inflation reduces what those pounds will buy, so for a real-terms view you could enter a rate roughly equal to your expected rate minus expected inflation — remembering that is only an approximation.