100% Free, Browser-Based Investment & Savings Growth Estimator.
Total Future Value
$0
after 20 years
Total Contributions
$0
incl. initial deposit
Total Interest Earned
$0
0% of final balance
Starting balance, deposits, interest and ending balance for each year.
| Year | Starting Balance | Contributions | Interest Earned | Ending Balance |
|---|
CompoundInterest is a free online compound interest calculator, investment growth calculator and future value calculator that runs 100% in your browser.
Initial deposit plus monthly or annual contributions, with daily, monthly, quarterly or annual compounding.
HTML5 Canvas stacked or line chart separating your deposits from compound interest over time.
Starting balance, contributions, interest earned and ending balance for every year, exportable to CSV.
All math runs locally on your device. No sign-up, no uploads and no backend server.
CompoundInterest is a free future value calculator that shows how a starting deposit and regular savings grow when interest is reinvested. Every calculation runs locally in your browser, so your figures stay private.
Compound interest is interest earned on your deposit and on interest already credited. Each period the rate applies to a larger balance, so growth speeds up the longer you stay invested — often called "interest on interest".
For a single deposit: A = P(1 + r/n)nt. With a regular payment PMT per period, add the future value of an annuity: PMT × [((1 + i)N − 1) / i], where i is the periodic rate and N the number of deposits.
Divide 72 by your annual rate to estimate how many years it takes to double your money. At 6% that's about 12 years; at 9%, about 8 years. The calculator shows both the Rule of 72 estimate and the exact doubling time.
More frequent compounding credits interest sooner, raising the effective annual rate (APY). The difference is real but modest — time in the market and contribution size matter far more.
| Compounding at 6% | Effective rate | $10,000 after 10 yrs |
|---|---|---|
| Annually | 6.000% | $17,908 |
| Quarterly | 6.136% | $18,140 |
| Monthly | 6.168% | $18,194 |
| Daily | 6.183% | $18,220 |
The balance is simulated month by month using the monthly equivalent of your chosen compounding rate, so the result matches P(1 + r/n)nt exactly for the initial deposit, and each contribution compounds from the month it is added.
Compound interest is interest earned on both your original deposit and on the interest already added to it. Each compounding period, interest is calculated on the new, larger balance, so growth accelerates over time. The formula is A = P(1 + r/n)nt, where P is the principal, r the annual rate, n the compounding periods per year and t the number of years.
With annual compounding the full annual rate is applied once per year. With monthly compounding the rate is divided by 12 and applied 12 times a year, so interest begins earning interest sooner. At 6% a year, annual compounding gives an effective yield of 6.00%, monthly about 6.17% and daily about 6.18%.
The Rule of 72 is a quick shortcut for estimating how long an investment takes to double: divide 72 by the annual interest rate. At 8% a year, money roughly doubles in 72 ÷ 8 = 9 years. It is most accurate for rates between about 6% and 10%.
Each contribution starts compounding from the moment it is deposited, so regular deposits add both the amount you put in and the interest those deposits earn. Over long periods, the interest earned on contributions often exceeds the contributions themselves.
APR is the nominal yearly rate before compounding. APY, also called the effective annual rate, includes compounding: APY = (1 + r/n)n − 1. CompoundInterest shows the effective annual rate for your chosen compounding frequency.
Yes. CompoundInterest is completely free and runs 100% in your web browser. No account is needed and none of the numbers you enter are sent to a server.
Results are pre-tax and pre-fee nominal estimates. Open Advanced options and enter an inflation rate to see the inflation-adjusted (real) value of your final balance in today's money.
Disclaimer: CompoundInterest provides estimates for educational purposes only and is not financial advice. Actual returns vary and are not guaranteed.