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Compound Interest Calculator

Compound interest is interest earned on both your original money and the interest already added. Enter a starting amount, an annual rate, the number of years and how often interest compounds; add a monthly deposit to see how regular saving changes the result.

Quick examples
$
%
years
$

Added at the end of each month. Leave at 0 for a single lump sum.

Your numbers stay in your browser. Nothing is uploaded.
Future balance$16,470.09
Interest earned
$6,470.09
Total paid in
$10,000.00
Effective annual rate (APY)
5.116%
What the balance is made of
  • Paid in
  • Interest
Growth year by year
YearPaid inInterest earnedBalance

Saved setups

Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.

    Your recent calculations

    Results you calculate here are kept on this device so you can come back to them.

      Formula

      Lump sum: A = P × (1 + r ÷ n)^(n × t)
      Continuous compounding: A = P × e^(r × t)
      With deposits: A = P × (1 + i)^m + D × ((1 + i)^m − 1) ÷ i, where i is the equivalent monthly rate and m the number of months
      APY = (1 + r ÷ n)^n − 1

      How to use it

      1. Enter the starting amount and the yearly interest rate.
      2. Enter the number of years and pick the compounding frequency.
      3. Add a monthly deposit if you will keep contributing.
      4. Read the future balance and the year-by-year table.

      Worked examples

      $10,000 at 5% compounded monthly for 10 years

      Future balance
      $16,470.09
      Interest earned
      $6,470.09
      Total paid in
      $10,000.00
      Effective annual rate (APY)
      5.116%

      $5,000 at 8% compounded annually for 20 years

      Future balance
      $23,304.79
      Interest earned
      $18,304.79
      Total paid in
      $5,000.00
      Effective annual rate (APY)
      8%

      $1,000 plus $200 a month at 6% compounded monthly for 10 years

      Future balance
      $34,595.27
      Interest earned
      $9,595.27
      Total paid in
      $25,000.00
      Effective annual rate (APY)
      6.168%

      How much compounding frequency matters

      Less than most people expect. $1,000 at 10% for one year grows to $1,100.00 compounded annually, $1,104.71 compounded monthly and $1,105.16 compounded daily. Rate and time matter far more than frequency.

      Time does the heavy lifting

      $10,000 at 7% compounded annually becomes $19,671.51 after 10 years, $38,696.84 after 20 and $76,122.55 after 30. The third decade adds almost four times as much as the first.

      Monthly deposits are assumed to arrive at the end of each month. When compounding is not monthly, the calculator converts the rate to the monthly rate that gives the same yearly growth.

      Questions people ask

      How much is $10,000 worth after 10 years at 5%?

      Compounded monthly it is $16,470.09, of which $6,470.09 is interest. Compounded annually it is $16,288.95.

      What is the compound interest formula?

      A = P(1 + r/n)^(nt): P is the principal, r the annual rate as a decimal, n the number of compounding periods per year and t the years. $5,000 at 8% compounded annually for 20 years is 5,000 × 1.08^20 = $23,304.79.

      How much will $200 a month grow to?

      Starting with $1,000 and adding $200 a month at 6% compounded monthly gives $34,595.27 after 10 years: $25,000 paid in and $9,595.27 of interest.

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