The Power of Compound Interest
Compound interest is the process where interest is calculated not only on your initial principal but also on the accumulated interest from previous periods. This creates an exponential growth curve that becomes increasingly powerful over time. It is the fundamental principle behind wealth building and long-term investment growth.
How Compound Interest Works
With compound interest, your money earns returns on both the original investment and all previously earned returns. For example, $10,000 invested at 7% annual return grows to $10,700 after one year. In year two, you earn 7% on $10,700 (not just $10,000), giving you $11,449. This compounding effect accelerates dramatically over longer periods. After 30 years, that same $10,000 grows to over $76,000 without any additional contributions.
The Rule of 72
The Rule of 72 is a simple shortcut to estimate how long it takes for an investment to double. Simply divide 72 by the annual interest rate. At 7% annual returns, your money doubles approximately every 10.3 years. At 10% returns, it doubles every 7.2 years. This rule highlights why starting to invest early is so powerful: more time means more doublings, and each doubling is on a larger base amount.
Monthly Contributions Supercharge Growth
Adding regular monthly contributions to compound interest creates explosive wealth growth. An initial investment of $10,000 with $200 monthly contributions at 7% return grows to approximately $44,700 after 10 years, $111,500 after 20 years, and $262,000 after 30 years. Our Compound Interest Calculator above lets you model different scenarios with varying initial investments, monthly contributions, return rates, and time horizons to visualize your wealth-building trajectory.