The Best Free Compound Interest Calculator Online
Albert Einstein supposedly called compound interest the “eighth wonder of the world.” It is the simple mathematical principle behind how regular people become millionaires by saving a small amount of money over a long period of time. The GadgetsFocus free online compound interest calculator helps you visualize exactly how your money will grow over decades.
How to Calculate Compound Interest
Our calculator updates instantly as you type. Simply fill in the four fields to see your financial future:
- Initial Balance: Enter the amount of money you currently have saved in your bank account, IRA, or brokerage account. (e.g., $10,000)
- Monthly Contribution: Enter how much new money you plan to invest every single month. (e.g., $500/month)
- Time Period (Years): Enter how many years you plan to leave the money invested before retiring or withdrawing it. (e.g., 30 years)
- Estimated Annual Return (APY): Enter the interest rate you expect to earn. Historically, the S&P 500 stock market index has returned about 7-10% per year on average. High Yield Savings accounts usually return around 4-5%.
How Does Compound Interest Work?
Imagine you invest $1,000 and earn 10% interest in year one. You make $100. You now have $1,100.
In year two, you don’t just earn 10% on your original $1,000. You earn 10% on the new total of $1,100. So in year two, you make $110. Your balance is now $1,210.
As the years go by, this “snowball effect” grows exponentially. Eventually, the interest you are earning every year becomes significantly larger than the actual money you are depositing! Our tool breaks down the math perfectly in the right-hand panel, showing you exactly how much money came from your deposits versus how much was generated purely by interest.