How to use the Compound Interest Calculator
- Enter your starting balance and how much you’ll add each month.
- Enter the expected annual return and the number of years.
- Choose how often interest compounds.
- See your future balance and a year-by-year table.
About this tool
Compound interest means you earn interest on your interest. Over long periods this snowball effect is powerful — it’s why starting to invest early matters more than investing large amounts later.
Rule of 72
Divide 72 by your annual return to estimate how many years it takes to double your money. At 8%, money doubles roughly every 9 years.
Typical returns
- High-yield savings: 3–5%
- Bonds: 3–6%
- US stock market (long-term average): around 7% after inflation, with large year-to-year swings
Frequently asked questions
What is compound interest?
Interest calculated on both your original money and the interest already earned.
Does compounding frequency matter much?
Slightly. Daily compounding earns a little more than monthly, but the rate and time invested matter far more.
Are investment returns guaranteed?
No. Stock returns vary each year; use this as an estimate, not a promise.