Compound Interest Calculator
See how your savings grow over time — with contributions and year-by-year breakdown
What Is Compound Interest?
Compound interest is interest earned on both your initial deposit and the interest already accumulated. Albert Einstein reportedly called it "the eighth wonder of the world." The key difference from simple interest: with compound interest, your money grows exponentially — slowly at first, then faster and faster as the interest itself earns interest.
The Rule of 72 gives you a quick estimate: divide 72 by your annual rate to find how many years it takes to double your money. At 7% interest, your money doubles roughly every 10 years. At 10%, it doubles every 7.2 years.
Monthly contributions matter enormously. Adding just $200/month to a $10,000 initial deposit at 7% for 20 years turns $10,000 into over $115,000 — compared to $38,697 without contributions. Time is the most powerful variable: starting 10 years earlier can double your final balance.