Number Compound Interest Calculator
Watch your money grow. Enter a starting deposit and monthly contribution to see your future balance, how much you contributed, and how much interest did the work — year by year.
| Total contributions | $0 |
| Interest earned | $0 |
| Year | Contributions | Interest | Balance |
How it works
Each month interest accrues on your balance at the monthly rate (annual rate ÷ 12), then your contribution is added — and it earns interest the very next month. That's compounding. The year-by-year table shows exactly how much of your balance came from your deposits versus growth.
Frequently asked questions
What is the Rule of 72?
Divide 72 by your annual rate to estimate how many years it takes money to double. At 7%, money doubles roughly every 10 years (72 ÷ 7 ≈ 10.3). Try 7% above and watch the balance nearly double the contributions over a decade.
Why does starting early matter so much?
Compounding is exponential: the last years do the heaviest lifting. Starting 10 years earlier at the same contribution can more than double your ending balance, because early money compounds the longest.
APY vs. APR — what's the difference?
APR is the simple annual rate before compounding; APY includes compounding, so it's slightly higher for the same nominal rate. This calculator compounds monthly, so the rate you enter behaves like an APY-style growth rate.
💵 Turn knowledge into a plan
Pair long-term growth with smart borrowing using the business loan calculator.