Compound Interest Calculator: Watch Your Money Grow
Einstein may or may not have called it the eighth wonder of the world, but compound interest really does change how you think about money. A dollar invested today is not just a dollar — it earns returns, and those returns earn returns. This calculator shows you exactly how that plays out over time, with any starting amount and interest rate you choose.
Compound Interest Calculator
See how your investment grows with compound interest over time.
How Compound Interest Works
Simple interest pays you a fixed amount on your original principal every year. Compound interest pays you interest on your principal AND on the interest you have already earned. In year one you earn interest on $10,000. In year two you earn interest on $10,000 plus last year’s interest. That gap between simple and compound grows dramatically over decades.
The compounding frequency matters too, but less than most people think. Monthly compounding versus annual compounding on a 7% rate adds only a fraction of a percent annually. What actually moves the needle: the rate itself, and the time horizon. Start ten years earlier and you roughly double your outcome.