Compound interest calculator
See how your savings and interest grow.
EstimateFinal balance
Estimate before tax and fees, assuming the rate stays the same. Not financial advice.
This compound interest calculator shows how an initial amount and monthly contributions grow when interest is added to your balance and then earns interest itself. It assumes the rate stays the same, and results are before tax and fees.
Year-by-year growth
Running totals at the end of each year: what you have paid in, the interest earned so far, and the balance.
| Year | Paid in ($) | Interest ($) | Balance ($) |
|---|---|---|---|
| 1 | 11,200.00 | 539.50 | 11,739.50 |
| 2 | 12,400.00 | 1,168.01 | 13,568.01 |
| 3 | 13,600.00 | 1,890.06 | 15,490.06 |
| 4 | 14,800.00 | 2,710.44 | 17,510.44 |
| 5 | 16,000.00 | 3,634.20 | 19,634.20 |
| 6 | 17,200.00 | 4,666.60 | 21,866.60 |
| 7 | 18,400.00 | 5,813.23 | 24,213.23 |
| 8 | 19,600.00 | 7,079.91 | 26,679.91 |
| 9 | 20,800.00 | 8,472.79 | 29,272.79 |
| 10 | 22,000.00 | 9,998.32 | 31,998.32 |
How the calculation works
Each month, interest is added to the balance, and your contribution is paid in at the end of the month. The balance after n months (the future value, FV) is:
FV = P × (1 + m)n + C × ((1 + m)n − 1) ÷ m
P = initial amount, C = monthly contribution, n = years × 12
Monthly compounding: m = annual rate ÷ 100 ÷ 12
Yearly compounding: m = (1 + annual rate ÷ 100)1/12 − 1
At 0%: FV = P + C × n
With monthly compounding, the monthly rate is the annual rate divided by 12, so over a year the balance grows slightly more than the stated rate. With yearly compounding, the calculator uses the equivalent monthly rate (1 + rate)1/12 − 1, so a full year grows by exactly the stated rate. Rounding happens only for display.
Example: you start with $10,000 and add $100 at the end of every month for 10 years (120 deposits) at 5% a year, compounded monthly. The monthly rate is 5% ÷ 12 = 0.4167%. After 10 years the balance is $31,998.32: $22,000.00 paid in and $9,998.32 interest.
Common questions
What is compound interest?
Compound interest means the interest you earn is added to your balance and then earns interest itself. Over short periods the effect is small, but over many years it can become a large part of the final balance. The table above shows how the interest share grows year by year.
What is the difference between monthly and yearly compounding?
With monthly compounding, the annual rate divided by 12 is added every month, so a year grows slightly more than the stated rate. With yearly compounding, this calculator uses a monthly rate chosen so that a full year grows by exactly the stated rate. Check which one your bank or fund quotes.
Are taxes and fees included?
No. Results are before tax on interest or gains and before account or fund fees, so what you keep can be lower. Tax rules depend on your country and the type of account. Fees reduce your return every year, so even small ones add up over long periods. Treat the result as an estimate, not financial advice.
Can I use this for investments?
Yes, as a rough guide, by entering an expected average annual return. Real investments do not grow at a constant rate: returns change from year to year and can be negative, so the actual result can be much higher or lower. Try a few different rates to see a range rather than a single number.
When are the monthly contributions added?
Contributions are added at the end of each month, so a contribution does not earn interest in the month it is paid. If you save at the start of each month instead, your result would be slightly higher. The initial amount earns interest from the first month onwards.
Why does my bank show a different balance?
Banks may credit interest daily, monthly or yearly, pay a variable rate, deduct tax or fees, or book deposits on different days. This calculator assumes a fixed rate, contributions at the end of each month and no tax or fees, so differences between its result and your statement are normal.
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Formula, self-tests and text last reviewed on 25 September 2026.
Results are estimates for planning and comparison. They are not a loan offer or financial advice; your lender's figures are the ones that count.