Simple vs Compound Interest: The Real Difference

Published June 2026 · 4 min read

Simple interest and compound interest sound similar — but the difference in your bank account is massive. Simple interest means you earn interest only on your original principal. Compound interest means you earn interest on your interest. Over long time horizons, the gap between simple and compound interest can be thousands of dollars.

The Numbers: USD 10,000 at 5% for 20 Years

Simple interest: USD 10,000 grows to USD 20,000. You earn exactly USD 500/year, every year. Compound interest (monthly): USD 10,000 grows to USD 27,130. The extra USD 7,130 comes entirely from earning interest on interest. That is 71% more money — just from compounding.

When Each One Applies

Simple interest is used for short-term loans, auto loans, and Treasury bills. Compound interest applies to savings accounts, CDs, retirement accounts, and credit card debt (yes — credit cards compound interest against you daily). Use our Simple Interest Calculator to compare directly against our Compound Interest Calculator.