Compound Interest Calculator
See how your money grows with compound interest and monthly contributions, year by year.
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| Final balance | 49,308.12 |
| Total contributed | 25,000 |
| Total interest | 24,308.12 |
Year-by-year growth
| Year | Total contributed | Total interest | Balance |
|---|---|---|---|
| 1 | 3,400 | 263.33 | 3,663.33 |
| 2 | 5,800 | 864.43 | 6,664.43 |
| 3 | 8,200 | 1,846.14 | 10,046.14 |
| 4 | 10,600 | 3,256.75 | 13,856.75 |
| 5 | 13,000 | 5,150.63 | 18,150.63 |
| 6 | 15,400 | 7,589.09 | 22,989.09 |
| 7 | 17,800 | 10,641.18 | 28,441.18 |
| 8 | 20,200 | 14,384.73 | 34,584.73 |
| 9 | 22,600 | 18,907.44 | 41,507.44 |
| 10 | 25,000 | 24,308.12 | 49,308.12 |
Quick answer: To calculate compound interest, enter the starting amount, the monthly contribution, the interest rate (monthly or annual) and the time frame. You'll see the final balance, how much you put in and how much came from interest, with a year-by-year table. Annual rates are converted to the equivalent monthly rate.
How to do it in 3 steps
- 1Enter the starting amount and monthly contribution.
- 2Set the rate and time frame.
- 3See the final balance and the table.
Why use Pronto Arquivo
Monthly contributions
Model investments with a deposit every month.
Monthly or annual rate
Converts the annual rate to its monthly equivalent, without the divide-by-12 mistake.
Year-by-year table
Watch the interest snowball over time.
Transparent math
Interest on interest, compounded monthly.
Guides
Formula
A = P × (1 + r)^n, plus the compounded contributions. With monthly deposits, each one earns its own interest until the end of the term. Example: $10,000 to start plus $500 a month at 7% a year for 20 years.
Real return
To account for inflation, use an inflation-adjusted rate or subtract expected inflation from the rate.
Frequently asked questions
How is compound interest calculated?
Amount = principal × (1 + rate)^time. The calculator does this month by month and adds your contributions.
What's the difference between simple and compound interest?
With compound interest, each month's interest earns interest the following month.
How do I convert an annual rate to monthly?
(1 + annual rate)^(1/12) − 1. A 12% annual rate is about 0.949% a month.
Does the calculator account for taxes?
No. The result is before taxes and fees.
