Compound interest calculator
How a starting balance and a monthly contribution grow when interest is compounded annually, quarterly, monthly, or daily.
By David Miller Updated Sources
Future value
$144,572.72
after 20 years
- Starting balance$10,000.00
- Contributions$48,000.00
- Interest$86,572.72
- Future value
- $144,572.72
- Starting balance
- $10,000.00
- Monthly contribution
- $200.00
- Contributions
- $48,000.00
- Interest earned
- $86,572.72
- Annual rate
- 7.00%
- Compounding
- monthly
- A $10,000.00 start, plus $200.00 added at the end of each month, grows to $144,572.72.
- Interest accounts for $86,572.72 of that ending balance.
Year 20: $144,572.72
- Balance
Year by year
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | $2,400.00 | $801.42 | $13,201.42 |
| 2 | $2,400.00 | $1,032.85 | $16,634.27 |
| 3 | $2,400.00 | $1,281.01 | $20,315.28 |
| 4 | $2,400.00 | $1,547.11 | $24,262.39 |
| 5 | $2,400.00 | $1,832.45 | $28,494.83 |
| 6 | $2,400.00 | $2,138.41 | $33,033.24 |
| 7 | $2,400.00 | $2,466.49 | $37,899.74 |
| 8 | $2,400.00 | $2,818.29 | $43,118.03 |
| 9 | $2,400.00 | $3,195.52 | $48,713.55 |
| 10 | $2,400.00 | $3,600.02 | $54,713.58 |
| 11 | $2,400.00 | $4,033.77 | $61,147.34 |
| 12 | $2,400.00 | $4,498.86 | $68,046.20 |
| 13 | $2,400.00 | $4,997.58 | $75,443.79 |
| 14 | $2,400.00 | $5,532.35 | $83,376.14 |
| 15 | $2,400.00 | $6,105.79 | $91,881.93 |
| 16 | $2,400.00 | $6,720.67 | $101,002.60 |
| 17 | $2,400.00 | $7,380.00 | $110,782.60 |
| 18 | $2,400.00 | $8,087.00 | $121,269.60 |
| 19 | $2,400.00 | $8,845.11 | $132,514.70 |
| 20 | $2,400.00 | $9,658.02 | $144,572.72 |
- The annual rate is nominal. Each month the balance grows by the monthly factor that matches the compounding frequency, and the contribution is added after that growth.
Future value
$144,572.72
How it works
Compound interest applies a growth factor to the whole balance, not only to the original deposit. This calculator steps one month at a time. The starting balance grows by the monthly factor that matches the compounding frequency you pick, then the contribution is added.
With monthly compounding the factor is one plus the annual rate divided by twelve. With the other frequencies, the factor is the monthly equivalent of compounding that many times a year. A zero rate skips the growth and the ending balance is the starting balance plus every contribution.
The year-by-year table shows the contributions added that year, the interest credited that year, and the balance at year end.
Formula
FV = P f^{12t} + PMT (f^{12t} - 1) / (f - 1), where f = (1 + r/n)^{n/12}
Worked example
Using the default inputs on this page.
- Starting balance
- $10,000.00
- Monthly contribution
- $200.00
- Annual rate
- 7.00%
- Years
- 20
- Compounding
- Monthly
Future value
$144,572.72
after 20 years
Questions
When is the monthly contribution added?
At the end of the month, after that month's growth. The contribution does not earn interest in the month it is deposited.
What does the compounding choice change?
The annual rate is nominal. Monthly compounding multiplies the balance by 1 plus the rate divided by 12. Annual, quarterly, and daily use the equivalent monthly factor for that frequency.
Is this a forecast of investment returns?
No. The rate is an assumption you type in. It is not a projection of stocks, bonds, or savings-account yields.
Sources
- Compound interest calculator U.S. Securities and Exchange Commission, Investor.gov. Retrieved 2026-10-11.