Compound Interest Calculator
See how savings or an investment grow when interest earns interest, with any compounding schedule and regular deposits.
About the Compound Interest Calculator
Compound interest is interest calculated on your original money plus the interest it has already earned. Each period the balance grows a little more than the last, so growth speeds up over time.
How often interest is added matters. Monthly compounding beats yearly compounding at the same quoted rate, which is why savings accounts often show both a rate and an APY (the effective yearly yield).
Regular deposits make the biggest difference over long periods: early deposits have the most years to compound.
The formula
A = P × (1 + r/n)^(n·t)
- A
- final amount
- P
- starting amount (principal)
- r
- yearly interest rate as a decimal (7% = 0.07)
- n
- number of times interest is added per year
- t
- number of years
Regular deposits add their own future value: D × ((1 + i)^N − 1) ÷ i, where i is the rate per deposit period and N the number of deposits. Continuous compounding uses A = P × e^(rt).
What 10,000 grows to at 7% a year
| Compounding | 10 years | 20 years | 30 years |
|---|---|---|---|
| Annually | 19,671.51 | 38,696.84 | 76,122.55 |
| Quarterly | 20,015.97 | 40,063.92 | 80,191.83 |
| Monthly | 20,096.61 | 40,387.39 | 81,164.97 |
| Daily | 20,136.18 | 40,546.56 | 81,645.26 |
| Continuously | 20,137.53 | 40,552.00 | 81,661.70 |
Any currency. More frequent compounding helps, but the jump from monthly to daily is small.
How to read your result
- Balance is what you'll have at the end, before tax and fees.
- The chart separates what you put in from what interest added; watch the interest share grow in later years.
- APY is the true yearly growth rate after compounding. Use it to compare accounts.
Worked example
$10,000 plus $200 a month at 7%, compounded monthly, for 10 years
- Total paid in = $34,000
- Interest earned = $20,713.58
- Final balance = $54,713.58
Things to keep in mind
- Assumes the same rate every year. Investment returns go up and down.
- Taxes on interest and account fees reduce real growth.
- Inflation lowers what the final amount will buy.
Questions people ask
How do I get textbook-style working (A = P(1 + R/100)ⁿ)?
Set the regular deposit to 0 and choose yearly, half-yearly or quarterly compounding, then switch to Learn step by step. A negative rate gives depreciation, A = P(1 − R/100)ⁿ.
What is the Rule of 72?
Divide 72 by the yearly rate to estimate how many years it takes to double your money. At 8%, 72 ÷ 8 = 9 years.
Is daily compounding much better than monthly?
Only slightly. At 7%, 10,000 grows to about 20,097 in 10 years monthly and 20,136 daily.
Should I deposit at the start or end of the month?
Depositing at the start gives each deposit one extra period of interest, so the result is a little higher.