Compound interest calculator
See how savings or an investment grow with compound interest, with optional regular deposits and a year-by-year breakdown.
- 100% free
- Runs in your browser
- No uploads
Final balance
Enter an amount, rate and number of years to see the growth.
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How to use the compound interest calculator
- Enter the starting amount, yearly rate and number of years. Choose how often interest is added: yearly, quarterly, monthly or daily.
- Add regular contributions if you save each month or year. Choose whether they go in at the start or the end of each period.
- Read the result and the table. The chart shows how much of each year's balance is money you paid in and how much is interest. The table below it has the exact figures, which you can also download as a CSV file.
How compound interest works
With compound interest, the interest you earn is added to the balance, and the next round of interest is worked out on that bigger balance. For a single deposit: A = P × (1 + r/n)^(n × t).
For regular contributions, the calculator steps through each month (or year) of deposits, grows the balance by the equivalent rate for that period, and adds each deposit at the start or end as chosen. Figures are kept unrounded and shown to the cent.
Worked examples
| Savings plan | Paid in | After 10 years |
|---|---|---|
| $10,000 at 5%, compounded yearly | $10,000 | $16,288.95 |
| $10,000 at 5%, compounded monthly | $10,000 | $16,470.09 |
| $10,000 at 5% monthly, plus $100 at the end of each month | $22,000 | $31,998.32 |
| $1,000 at the end of each year at 7%, compounded yearly | $10,000 | $13,816.45 |
Things to keep in mind
Time does most of the work. In the third example, interest is $9,998.32 of the final balance. Leave it for 20 more years at the same rate and interest becomes the larger share by far.
Rates change. Savings rates move, and investment returns go up and down from year to year. A fixed rate here is a simplification, so treat the result as an estimate, not a promise or financial advice.
Fees, taxes and inflation aren't included. A 1% yearly fee or tax on interest lowers the result noticeably over long periods, and inflation reduces what the final amount will buy.
Frequently asked questions
What is the compound interest formula?
A = P × (1 + r/n)^(n × t), where P is the starting amount, r is the yearly rate as a decimal, n is how many times a year interest is added, and t is the number of years. $10,000 at 5% compounded monthly for 10 years: 10,000 × (1 + 0.05/12)^120 = $16,470.09.
Does compounding more often make a big difference?
Less than people expect. $10,000 at 5% for 10 years grows to $16,288.95 with yearly compounding, $16,436.19 quarterly, $16,470.09 monthly and $16,486.65 daily. The rate and the time matter far more.
What's the difference between adding money at the start or end of a period?
A deposit made at the start of the month earns interest for that month; one made at the end doesn't. $100 a month for 10 years at 5% compounded monthly grows to $15,592.93 with deposits at the start and $15,528.23 at the end.
How are monthly deposits handled with yearly or daily compounding?
The calculator converts the yearly rate into the equivalent rate for each deposit period, so every dollar grows at the same effective yearly rate however often interest is added. Banks may credit interest on mid-period deposits slightly differently, so treat small differences as rounding.
How long does it take money to double?
A quick estimate is the rule of 72: divide 72 by the yearly rate. At 6% that's about 12 years, and indeed 1.06^12 = 2.01.