Albert Einstein reportedly called compound interest "the eighth wonder of the world." Whether or not he actually said it, the power of compound interest is undeniable — it's the key mechanism behind long-term wealth building.
What Is Compound Interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (calculated only on the principal), compound interest grows exponentially over time.
The Compound Interest Formula
A = P(1 + r/n)^(nt), where A = final amount, P = principal, r = annual interest rate, n = compounding frequency per year, t = time in years.
Example: The Power of Starting Early
If you invest $10,000 at 7% annual return: After 10 years: $19,672. After 20 years: $38,697. After 30 years: $76,123. The money nearly doubles every decade without adding a single dollar.
Compounding Frequency Matters
The more frequently interest compounds, the more you earn. Daily compounding yields slightly more than monthly, which yields more than annually.
Use Our Free Compound Interest Calculator
Our calculator lets you input principal, interest rate, compounding frequency, time period, and monthly contributions. It generates a detailed growth chart showing your wealth trajectory. Perfect for retirement planning, savings goals, and investment comparisons.