How to use the Compound Interest Calculator
- Enter your starting balance and how much you’ll add each month.
- Set the expected yearly interest rate or return and the number of years.
- Choose how often interest compounds — monthly is common for savings accounts.
- Read the future balance and the year-by-year table, or download it as CSV.
The compound interest formula
With compound interest you earn interest on your interest. For a single deposit the future value is A = P × (1 + r/k)k·t, where P is the starting amount, r the yearly rate, k the number of compounding periods per year and t the years. $10,000 at 7% compounded monthly grows to about $40,000 in 20 years.
Regular contributions are added month by month in this calculator, with each month’s interest worked out from the compounding you choose, so mixed setups (monthly deposits, daily or yearly compounding) come out right.
The rule of 72
A quick way to estimate growth: divide 72 by the yearly rate to get the years it takes money to double. At 6% it doubles in about 12 years; at 9% in about 8.
Keep in mind
- Investment returns vary from year to year; a fixed rate is an average, not a promise.
- Inflation lowers what the future balance can buy — subtract an inflation estimate from the rate to see the result in today’s money.
- Taxes and fees reduce growth and aren’t included.
Paying a loan instead? Use the Loan Calculator or the Mortgage Calculator.
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Tools that pair well with the Compound Interest Calculator
- Percentage Calculator — Seven everyday percentage calculations on one page.
- Age Calculator — Enter a date of birth to get the exact age in years, months and days — plus total days and weeks lived, the weekday you were born on, a countdown to the next birthday and your star sign.
- Date Difference Calculator — Count the days between two dates — including business days and a years/months/days breakdown — add or subtract time from a date, or run a live countdown.
- Roman Numeral Converter — Convert any number from 1 to 3,999,999 into Roman numerals — or read Roman numerals back as numbers — with a breakdown of every symbol.