Compound Interest Calculator
Use this compound interest calculator to see how a savings balance grows when interest is added to the amount you already have. You can enter a starting amount, an optional monthly deposit, an annual interest rate, a number of years and how often the interest compounds.
The calculator shows the balance at the end, the total you put in and the interest earned. It also builds a year-by-year table so you can see how the balance changes over the whole period. The results are a mathematical illustration, so check the figures with your bank or lender before making decisions.
Year-by-year schedule
How to use the compound interest calculator
- Enter your starting amount in pounds. For example, £10,000.00.
- If you plan to add money each month, enter the amount in the 'Added every month' box. Leave it at zero if you will not add anything.
- Enter the annual interest rate as a percentage. For example, 5%.
- Enter the number of years you want the savings to grow for. For example, 10 years.
- Choose how often the interest compounds from the list. For the worked example, this is Monthly.
- Read the balance at the end, the total put in and the interest earned, then check the year-by-year table for the full picture.
The formula
- Monthly growth rate i = (1 + annual rate ÷ 100 ÷ c) ^ (c ÷ 12) − 1, where c is how often interest compounds a year
- Each month: balance = balance × (1 + i) + the monthly deposit (added at the end of the month)
Worked example
The figures below are made up to show the maths. They are not current prices, rates or product figures.
| Starting amount | £10,000.00 |
|---|---|
| Added every month | £200.00 |
| Annual interest rate | 5% |
| Years | 10 years |
| Compounding | Monthly |
- Balance at the end £47,526.55
- Total put in £34,000.00
- Interest earned £13,526.55
Tips for an accurate answer
- Make sure the interest rate you enter is the annual rate, not a monthly one, so the result matches what your account states.
- Check whether your account compounds monthly, yearly or on another schedule, as this changes the result.
- Remember that monthly deposits are added at the end of each month in this calculator, which can differ slightly from a real account.
- Use the total put in figure to compare how much of the final balance came from your own payments and how much came from interest.
- Confirm the final figures with your bank or savings provider, since fees, tax and rate changes are not included here.
Questions people ask
How do I work out monthly compound interest?
Choose Monthly in the compounding box and enter your starting amount, annual interest rate and number of years. The calculator adds interest each month and shows the balance at the end. The worked example on this page uses monthly compounding.
Is there an official government compound interest calculator?
This page is an independent calculator and is not an official government tool. It shows how savings grow using the figures you enter. For figures specific to a government product, check the official guidance or your provider.
Can I use this calculator to see how savings grow by age?
The calculator works from years rather than age, so enter the number of years you want to save for. For example, if you plan to save until a certain age, enter the number of years between now and then. The year-by-year table shows the balance at each step.
Can this calculator work out daily compounding?
This calculator offers a choice of compounding frequencies from the list provided. Select the option that most closely matches your account, and check with your bank if you need a daily figure.
What does this compound interest calculator work out?
It works out how a savings balance grows over a set number of years when interest is added regularly and optional monthly deposits are included. It shows the balance at the end, the total you paid in and the interest earned. A year-by-year table shows how the balance builds up.
What is the monthly deposit box for?
The 'Added every month' box is for money you plan to put into the account each month on top of the starting amount. The calculator adds this deposit at the end of each month. If you do not plan to add anything, leave it at zero.
Why does the compounding frequency matter?
Compounding frequency decides how often interest is added to the balance, and interest added earlier can earn interest of its own. Choosing monthly, for example, gives a different result from choosing yearly with the same rate. Pick the option that matches how your account works.
How much did the worked example grow?
In the worked example, a starting amount of £10,000.00 with £200.00 added every month at 5% over 10 years, compounded monthly, gives a balance of £47,526.55. Of this, £34,000.00 was put in and £13,526.55 was interest.
Sources
This calculator uses the standard loan and interest formulas above and the numbers you type. It needs no outside figures.
An estimate from the numbers you enter, worked out with the formula shown. It is maths, not financial advice: your lender or bank has the final figures. Page checked 23 Oct 2026. Read the disclaimer