How Personal Loan Interest Is Calculated: A Clear Breakdown Understanding how lenders calculate interest on personal loans helps you compare offers and estimate true borrowing costs. In this guide, we’ll demystify key terms and walk through the formula so you know exactly what you’ll pay. Table of Contents 1. APR vs. Interest Rate 2. Simple Interest Formula 3. Impact of Amortization 4. Step-by-Step Example 5. Tips to Lower Your Interest Cost 1. APR vs. Interest Rate The interest rate is the annual cost charged by the lender, while the APR includes both rate and fees (origination, closing) spread over the term—giving a more complete picture of your cost. 2. Simple Interest Formula Most personal loans use simple interest: Interest = Principal × Rate × Time Where “Time” is the fraction of the year you borrow (e.g., 36 months = 3 years). 3. Impact of Amortization Amortization spreads principal and interest into fixed monthly payments. Early payments inclu...