Compound Interest Calculator Free · Calc Pro
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Coming soonFind out what your savings or investment will grow to, or work backwards to the rate or time you need to hit a target. Calc Pro's Compound Interest worksheet solves for whichever of the four values you leave out.
How to use the Compound Interest Calculator
- 1Tap # of Periods and enter how many periods the money grows for, such as 10 years.
- 2Press ↓ and enter the Interest rate per period (7 for 7%) and the Start Value.
- 3Tap Final Value and press Calc to see what it grows to.
- 4To solve for something else, enter the other three values, tap the one you want, such as Interest rate, and press Calc.
How compound interest works
With simple interest you earn the same amount every year. With compound interest, each year's interest is added to the balance, so you earn interest on your interest:
Final value = Start value × (1 + r)ⁿ
At 7%, $10,000 earns $700 in the first year but $1,286.92 in the tenth, because by then the balance has grown to $18,384.59.
| Year | Balance at 7% |
|---|---|
| 0 | $10,000.00 |
| 5 | $14,025.52 |
| 10 | $19,671.51 |
| 20 | $38,696.84 |
| 30 | $76,122.55 |
The longer the money compounds, the faster it grows, which is why starting early matters so much.
Solve for any value
Enter any three of the four values, tap the one you want and press Calc:
- Final Value: what your money grows to
- Interest rate: the return you need to reach a target
- Start Value: how much to invest today to reach a target
- # of Periods: how long it takes to reach a target
Frequently Asked Questions
What is the compound interest formula?
Final value = Start value × (1 + r)^n, where r is the interest rate per period and n is the number of periods. Each period's interest is added to the balance, so the next period earns interest on it too.
How do I calculate monthly compounding?
The worksheet compounds once per period, so use months as the periods and the monthly rate. For 5% a year compounded monthly over 10 years, enter 120 periods at 0.4167% (5 ÷ 12).
How long does it take to double my money?
Enter the start value, a final value twice as large and the rate, then tap # of Periods and press Calc. As a quick check, the rule of 72 says money doubles in about 72 ÷ rate years: about 10.3 years at 7%.
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