Compound interest calculator
See how a starting amount and regular monthly deposits grow with compound interest, and how much of the final balance is interest.
How it works
Without deposits, an amount P at a yearly rate r compounded k times a year grows in t years to:
A = P × (1 + r/k)^(k × t)The calculator also adds the monthly contribution at the end of every month and lets it earn interest from then on.
Worked example
$10,000 at 6% compounded monthly for 10 years, no deposits:
- 1 + 0.06 ÷ 12 = 1.005
- 1.005^120 = 1.8194
- 10000 × 1.8194 = $18,193.97
Frequently asked questions
What is compound interest?
Interest that is added to the balance and then earns interest itself. The more often it is compounded, the faster the balance grows, although the difference between monthly and daily is small.
When are the monthly contributions added?
At the end of each month, after that month’s interest. Contributions made at the start of the month would grow slightly more.
What is the rule of 72?
A quick estimate of how long money takes to double: 72 divided by the yearly rate. At 6% that is about 12 years.
Are taxes and inflation included?
No. The result is the nominal balance before taxes, fees and inflation.