Compound Interest Calculator

Worked example

A starting amount of 1,000 at 5% a year, compounded annually for 1 year, grows to 1,050, which is 50 in interest. The same 1,000 compounded monthly for 10 years grows to about 1,647.01.

How we calculated this

Final amount = starting amount × (1 + annual rate ÷ periods a year) raised to the power of (periods a year × years). Interest earned is the final amount minus the starting amount. The rate is taken as a nominal yearly rate that stays the same for the whole time, and a year has 365 days when compounding daily.

This is plain mathematics on the numbers you enter. It does not include deposits, withdrawals, tax, fees or inflation, and it does not describe any account or investment. It is not a forecast and it is not advice.

When the number of periods is a whole number the result is worked out exactly. When it is not, for example 1.3 years compounded monthly, or when the exact value would be very long, the result is worked out to about 15 significant digits and is shown with the approximate sign.

A result written as a plain number is exact. A result starting with “≈” has been rounded to 10 significant figures, because its exact decimal never ends or is too long to read comfortably. When an exact value is long, its full digits are shown underneath. The calculation itself is never rounded: only the display is.