Compound interest calculator. Watch savings snowball.

How to use the Compound Interest Calculator

This calculator projects how a balance grows when interest is added back to it and you keep paying in. It steps through your plan month by month, adds each contribution, applies interest at your chosen compounding interval and totals every year. Use it for savings goals, retirement estimates or to compare two rates.

Step by step

1. 1
   Choose a currency

   Pick a symbol from Currency: $, €, £, ₹, ¥, A$, C$ or None. It only changes the symbol shown next to the amounts. No exchange rate is applied.

2. 2
   Enter what you start with

   Type your starting amount in Initial principal. The page opens with an example of 10,000. Enter 0 if you are starting from nothing.

3. 3
   Add regular contributions

   Enter an amount in Regular contribution and choose per month or per year beside it. The example adds 200 per month. Monthly amounts land at the end of every month, yearly amounts at the end of each full year.

4. 4
   Set the rate and the time

   Enter the Annual interest rate % (example 7) and the Time horizon (years) (example 20). Fractions work, so 2.5 years is 30 months. The horizon must be above zero and no more than 100 years.

5. 5
   Pick the compounding frequency

   Choose Monthly, Quarterly or Annually under Compounding frequency to match your account. Interest is added that many times a year, at the annual rate divided by the number of periods.

6. 6
   Read or export the table

   Scroll to the Year-by-year breakdown and press Export CSV to download compound-interest-schedule.csv with the year, start balance, contributions, interest and end balance for every row.

Reading the result

• Future value is the balance at the end of the horizon. The example, 10,000 plus 200 a month at 7% for 20 years compounded monthly, ends at $145,180.47.
• Total contributions is your principal plus every deposit, $58,000 in the example. Interest earned is the rest, $87,180. Money multiple divides the future value by total contributions, so 2.5× means every dollar paid in became 2.50.
• The chart plots the balance as a green line over a shaded area and your running total of contributions as a dashed amber line. The gap between the two is the interest.
• Each table row covers one year. If the horizon is not a whole number of years, the last row is a partial year labeled with its fraction, such as 2.5.

Tips and common mistakes

• Enter the rate as a plain number, 7 for 7%, not 0.07.
• Switch between Monthly and Annually to see what compounding frequency alone is worth. In the example, monthly compounding ends about 1,207 higher than annual.
• Yearly contributions only land at the end of each full year, so a partial final year gets no yearly deposit.
• The projection uses one fixed rate and leaves out tax, fees and inflation. Treat it as a planning figure, not a forecast.
• If a message shows instead of a number, check that the rate and years are filled in, that no amount is negative and that the horizon is 100 years or less.

Privacy and limits

Every figure is calculated in your browser and nothing is sent anywhere. The calculator saves nothing, so the example values come back when you reload, and the CSV file is created on your device.

Back to the tool

Everything a projection should show.

• Project a lump-sum investment over any horizon up to 100 years, including fractional years, at a chosen annual rate.
• Add monthly or yearly contributions and see how consistent saving accelerates growth against interest alone.
• Compare compounding frequencies, monthly, quarterly or annual, and watch the end balance shift instantly.
• Read the year-by-year table: start balance, contributions, interest earned and end balance for every year, partial final year included.
• Export the full schedule as CSV for a spreadsheet or financial model, and read the money-multiple at a glance.
• Switch currency symbols (USD, EUR, GBP, INR, JPY, AUD, CAD or none) to match your region.

Frequently asked questions.

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