Compound Interest Calculator

Calculates how a starting amount and regular deposits grow with compound interest over a number of years. Use it to see the final balance of savings or an investment plan, how much of it is interest, and how long money takes to double.

How to use

1. Enter the "Starting amount" and "Regular deposit", then choose "Deposit every" and "Deposit at the".
2. Enter the "Annual interest rate or return" and "Number of years" (1 to 100), and choose the "Compounding".
3. Read the "Final balance", "Total deposited" and "Interest earned". Add an "Inflation rate" to also see the result "In today's money".
4. Use the "Growth over time" chart and the "Year by year" table, and press "Save as CSV" to download the table.

How it works

• Compound interest means interest is also earned on earlier interest. Compounding n times a year turns an annual rate r into an effective annual rate of (1 + r/n)^n − 1.
• A deposit at the start of a period earns one more period of interest than a deposit at the end.
• The rate is an assumption, not a guaranteed return. This is a planning aid, not financial advice. Taxes and fees are not included.

Questions and answers

What is the compound interest formula?

Amount = principal × (1 + rate ÷ n)^(n × years), where n is the number of times interest is added each year. 1,000 at 10% compounded yearly for 2 years becomes 1,210.

What is the rule of 72?

Divide 72 by the annual rate in percent to estimate the years needed to double your money. At 6% that is about 12 years; the page also shows the exact figure.

How much difference does monthly compounding make?

At the same annual rate, more frequent compounding gives a slightly higher effective rate. 12% a year compounded monthly is an effective rate of about 12.68%.

How is compound interest different from simple interest?

Simple interest is paid only on the principal, while compound interest is also paid on interest already earned. So the interest added each year keeps growing, which the "Year by year" table shows.