📈 Compound Interest Calculator
Quick answer
Compound interest earns interest on interest: A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the compounding frequency per year and t the years. Regular monthly contributions grow as an annuity on top of the principal. Because growth is exponential, time in the market matters more than the amount added later.
The starting amount compounds at the chosen frequency; monthly contributions are added at the end of each month and compounded monthly.
Future value after 10 years
| Initial amount | 10,000.00 |
| Total contributions | 12,000.00 |
| Interest earned | 18,491.01 |
Growth by year
| Year | Deposited | Interest earned | Balance |
|---|---|---|---|
| 1 | 11,200.00 | 874.99 | 12,074.99 |
| 2 | 12,400.00 | 1,922.20 | 14,322.20 |
| 3 | 13,600.00 | 3,155.93 | 16,755.93 |
| 4 | 14,800.00 | 4,591.65 | 19,391.65 |
| 5 | 16,000.00 | 6,246.14 | 22,246.14 |
| 6 | 17,200.00 | 8,137.55 | 25,337.55 |
| 7 | 18,400.00 | 10,285.55 | 28,685.55 |
| 8 | 19,600.00 | 12,711.43 | 32,311.43 |
| 9 | 20,800.00 | 15,438.26 | 36,238.26 |
| 10 | 22,000.00 | 18,491.01 | 40,491.01 |
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How to use the Compound Interest Calculator
- Enter your starting amount and any monthly contribution.
- Enter the expected annual interest rate.
- Set how many years the money will grow.
- Choose how often interest compounds — yearly, quarterly, monthly or daily.
- Click "Calculate growth" for the future value, interest earned and a year-by-year table.
Frequently asked questions
What is the compound interest formula?
A = P(1 + r/n)^(nt): P is the starting amount, r is the annual interest rate as a decimal, n is how many times interest compounds per year, and t is the number of years. With monthly contributions, each deposit compounds for the months it stays invested.
Does compounding frequency matter much?
It helps, but modestly. On 10,000 at 8% for 10 years, yearly compounding gives about 21,589, monthly about 22,196 and daily about 22,253 — the bigger levers are the rate, the contributions and the time.
What is the Rule of 72?
Divide 72 by the annual interest rate to estimate how many years money takes to double. At 8%, money doubles in roughly 72 ÷ 8 = 9 years.