1. Your numbers
2. Your results
- Starting amount—
- Your monthly additions—
- Interest earned—
Estimate only. Assumes a steady rate and additions at the end of each month. Real returns go up and down.
What Is Compound Interest? How Does It Grow Your Money?
Compound interest means you earn interest on your money, and then you earn interest on that interest too. Your money grows on top of its own growth, like a tree that adds new branches every year.
Enter a starting amount, how much you’ll add each month, an interest rate, and how many years. The calculator shows your total, how much of it is interest, and a chart of your money growing year by year.
Time matters most. The longer your money has to grow, the faster it speeds up. Starting early with small amounts often beats starting later with bigger ones.
The interest rate is a best guess. Savings accounts pay lower rates. Investments can grow faster over time, but they go up and down and are never guaranteed.
The Formula
Interest = balance × rate. Next time, you earn interest on the new, bigger balance.
Example: Put in $100 a month for 10 years at 7%, and you’ll have about $17,300. You only put in $12,000, so about $5,300 is interest your money earned on its own.
Tip:
What rate should I use? For a savings account, use the APY your bank lists. For long-term investing, try a few different rates to see a range of what could happen.