Calculate compound interest on your savings
Enter a starting amount, a yearly rate and a number of years to see what your savings or investment could grow to, with or without a monthly deposit.
Calculations run on this device. We don't see, store or log the amounts you enter.
How it works
- Enter the starting amount, the yearly rate and the number of years.
- Choose how often interest is added, and a monthly deposit if you make one.
- Read the final amount, what you deposited and the interest earned; open the table for each year.
The formula
Without deposits, final amount = P × (1 + r/n)^(n×t): P is the starting amount, r the yearly rate, n how many times a year interest is added and t the years. 10,000 at 8% a year compounded monthly for 10 years grows to 22,196.40; compounded yearly it reaches 21,589.25.
Monthly deposits
Deposits are added at the end of each month, and the chosen compounding is converted to the equivalent monthly rate so both work together. Adding 100 a month to the example above gives 40,491 after 10 years: 22,000 deposited and 18,491 earned.
Good to know
The results assume a constant rate and no tax, fees or inflation; real returns vary year to year. The rule of 72 gives a quick check: at 8%, money doubles in about 72 ÷ 8 = 9 years.
Worked examples
| Starting amount | Yearly rate | Years | Compounding | Monthly deposit | Final balance | Interest earned |
|---|---|---|---|---|---|---|
| 10,000 | 5% | 10 | Yearly | – | 16,288.95 | 6,288.95 |
| 10,000 | 5% | 10 | Monthly | – | 16,470.09 | 6,470.09 |
| 10,000 | 5% | 10 | Daily | – | 16,486.65 | 6,486.65 |
| 5,000 | 8% | 20 | Monthly | – | 24,634.01 | 19,634.01 |
| 0 | 6% | 10 | Monthly | 500 | 81,939.67 | 21,939.67 |
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is paid only on the starting amount; compound interest is also paid on interest already earned, so growth speeds up over time.
Does compounding frequency matter much?
A little: at 8% for 10 years, monthly compounding gives 22,196 on 10,000 against 21,589 yearly, about 3% more.
Can I use it for profit-sharing savings accounts?
Yes, as an estimate: enter the expected yearly profit rate. Actual profit on such accounts changes from month to month.
Sources
Last reviewed: September 30, 2026
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