Enter the interest rate and the period to see the result.
How interest is calculated
With compound interest, each month’s interest is added to the balance and then earns interest itself: balance = previous balance × (1 + monthly rate) + contribution. With simple interest the rate applies only to the money you put in, so interest grows in a straight line.
For compound interest an annual rate is converted to the equivalent monthly rate, (1 + annual rate)^(1/12) − 1; for simple interest it is divided by 12. Your numbers never leave your browser.
Interest calculator: frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original amount. Compound interest is calculated on the amount plus the interest already earned, so it grows faster over time.
How do monthly contributions change the result?
Each deposit is made at the end of the month and starts earning interest the following month, so regular contributions can add up to far more than the initial amount alone.
Does the result include taxes or inflation?
No. The result is a gross estimate. Taxes, fees and inflation reduce the real return, so check the rules of your investment.