Compound Interest Calculator
See how savings or an investment grow with compound interest: a starting amount, regular contributions, any compounding frequency, and a year-by-year table, compared with simple interest.
Pay the same amount every month or year, as with an instalment savings account or a savings plan. The payment made on opening is payment 1.
Paid once, on opening. Do not include payment 1 of the regular deposits.
Balance at the end of each year
Year by year
| Year | Contributions | Interest | Balance |
|---|
How the growth is calculated
- A single amount grows to P × (1 + r ÷ n)^(n × t), with r the annual rate, n the compounding periods per year and t the years. Simple interest is P × (1 + r × t).
- The calculator works month by month: the balance grows by (1 + r ÷ n)^(n ÷ 12) each month, and a contribution earns the same rate from the month it is paid in. A bank that credits interest only on set dates pays slightly less on money paid in between them.
- Taxes on interest, fees, inflation and changes in the rate are not included.
- Everything runs in your browser. The amounts you enter are not sent to LeedyBox or saved.
Wrong result? If a figure looks wrong, email us what you entered and the figure you expected, so we can check it.
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How to use
- Choose what to calculate: regular deposits, a lump sum, or both, and enter the amounts. Type digits only: separators are added for you, and currencies without cents, such as the won and the yen, take no decimals.
- Type the annual interest rate and the time in years and months.
- Choose how often interest is added, as stated in the terms of your account or product; pick "None" to see simple interest.
- Read the final balance, the money you paid in and the interest earned. The chart and the table show every year; "Copy table" copies it for a spreadsheet.
Frequently asked questions
What is compound interest?
Interest that is added to the balance and then earns interest itself. With simple interest only the money you paid in earns interest, so the gap between the two grows every year.
How do I calculate compound interest?
A single deposit grows to P × (1 + r ÷ n)^(n × t). For example, 10,000 at 5% compounded yearly for 10 years becomes 10,000 × 1.05^10 = 16,288.95.
How much difference does the compounding frequency make?
Less than the rate itself. At 5%, yearly compounding gives an effective 5%, monthly 5.116% and daily 5.127%. The effective annual rate (APY) shown under the result makes offers comparable.
When is the first payment made?
By default on opening, as with an instalment savings account: over 3 years that is payment 1 on opening and 35 more, 36 in all, the last one a month before maturity. If you start one month after opening, for example from your salary, choose "One period after opening"; each payment then earns one month less interest.
What is the rule of 72?
A shortcut: 72 ÷ the annual rate gives roughly the years needed to double the money, so about 10 years at 7.2%. The calculator shows the exact doubling time for the rate and compounding you chose.
Is what I enter sent anywhere?
No. The calculation runs in your browser, and the page does not save the amounts you enter.