Economics
Compound Interest
Quick fact
Albert Einstein reportedly called compound interest the 'eighth wonder of the world,' saying 'He who understands it, earns it; he who doesn't, pays it.'
Why this is interesting
Have you ever wondered why starting to save just a few years earlier can lead to dramatically more money later—even if you save less overall?
Read the full explanation
Understanding Compound Interest
Imagine you have $100 in a savings account that pays 10% interest each year. After one year, you earn $10, making the total $110. In the second year, interest is paid not just on your original $100, but on the entire $110—so you earn $11, giving you $121. Over time, this 'interest on interest' accelerates growth like a snowball rolling downhill. The longer the money is left to compound, the faster the balance grows. This is why even small amounts saved early can outpace larger amounts saved later.
A deeper explanation
Compound interest works because each interest payment becomes part of the principal for the next period. The mathematical formula is A = P(1 + r/n)^(nt), where A is the future value, P is principal, r is annual interest rate, n is number of compounding periods per year, and t is time in years. The key insight is that the exponent (nt) makes growth exponential rather than linear. Higher compounding frequency (e.g., daily vs. annual) accelerates growth. This concept matters enormously: it explains how retirement accounts can grow, how credit card debt can spiral, and why time is the investor's greatest ally. Understanding compound interest empowers people to make smarter choices about saving, borrowing, and investing.