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Compound Interest Time Calculator

Find out how many years it takes to reach a target amount. Enter your principal, goal future value, and annual rate to solve for the time with yearly compounding.

Input

$
$
%

Result

Years needed to reach the target (3% annual, yearly compounding)

23.4yrs

About 23 yr 5 mo

Principal

$1,000,000.00

Future value

$2,000,000.00

Interest

$1,000,000.00

How it works

  • Starting from the yearly compound future-value formula future = principal x (1 + rate)^years, we solve for the time, giving n = ln(future / principal) / ln(1 + rate).
  • The percentage rate is converted to r = rate / 100, and the natural logarithm (ln) is used to find the continuous number of years as a decimal.
  • That decimal is split into whole years plus the fractional part multiplied by 12 and rounded to months, shown as 'about X yr Y mo' (when months reach 12 they roll over into the next year).
  • Interest is computed as future value minus principal and shown on the stat cards alongside the principal and future value.
  • Principal and future value must be greater than 0, the annual rate must be greater than 0 and up to 100, and the future value must exceed the principal (otherwise the logarithm is undefined and an error is shown).
  • This tool assumes once-a-year (annual) compounding and gives an estimate. Real financial products may differ due to compounding frequency, taxes, fees, and rate changes, so make investment decisions at your own discretion.