About the Compound Interest Calculator
This free compound interest calculator helps people in the United States get a quick, private estimate before they talk to a lender, insurer, employer or advisor. There is no signup, nothing is stored on our servers and every result updates instantly in your browser.
How this calculator works
Future value combines growth on your starting amount, P*(1+i)^k, with a series of monthly deposits, c*((1+i)^k - 1)/i, where i is the monthly rate and k the number of months.
Worked example
$5,000 plus $300 monthly at 7% for 20 years grows to roughly $176,000, of which about $77,000 is deposits. Change any input above to see how the result moves, which is the fastest way to understand which factor matters most for you.
Tips to get a better result
Time matters more than amount. Start early, deposit regularly and avoid high fees. Returns are not guaranteed, and past performance does not predict future results.
Key factors that change your result
Time is the strongest factor: the same deposits grow far more over 30 years than 20. Returns are not guaranteed, so test lower rates too. Fees, taxes and inflation reduce real growth, so treat the result as a projection, not a promise.
Accuracy and limits
Every calculator on 100tools uses standard published formulas combined with average US market assumptions. Real offers depend on your credit profile, state, provider and personal circumstances, so treat the output as a starting point and confirm with an official quote or a licensed professional. Read more on our methodology page.
Frequently asked questions
What is compound interest?
Interest earned on both the original amount and previously earned interest.
Is 7% realistic?
It is close to the long-run inflation-unadjusted US stock market average but returns vary widely year to year.
Is the compound interest calculator free to use?
Yes. Every calculator on 100tools is free with no registration.
Do you store the numbers I enter?
No. Calculations run in your browser and nothing you type is sent to our servers.