The Flat Rate Formula
Simple interest formula: Total Interest = Principal × Annual Rate × Duration (Years).
Because you keep paying interest on money you already repaid, flat rate loans carry a much higher effective Annual Percentage Rate (APR).
Simple (Flat) Interest Explained: Formula and Calculation
Learn how flat simple interest is calculated on the original principal and why a 5% flat rate is equivalent to nearly a 9% to 10% effective APR.
💡 Key Takeaways
- Simple flat interest calculates interest on initial principal for the full loan life, ignoring monthly repayments.
- Because actual outstanding principal decreases every month, a flat rate significantly underestimates effective cost.
- Reducing-balance APR is roughly 1.8x to 1.9x the stated flat rate.
Related Financial Calculators
Simple vs Reducing Balance Interest Calculator
Compare simple flat interest vs reducing balance amortization to understand how lenders calculate interest charges.
🧮 Open Simple vs Reducing Balance Interest Calculator →Related Educational Guides
What Is APR? Annual Percentage Rate Explained Simply
Learn what APR (Annual Percentage Rate) means, how it includes both interest and compulsory fees, and why it is the true measure of borrowing cost.
Reducing Balance Interest Explained: Why It Is Fairer for Borrowers
Understand how reducing balance interest charges interest strictly on remaining debt, ensuring you only pay for money you currently hold.
⚠️ Educational Resource Only
All values are mathematical estimates for educational purposes only. Actual lender terms and fees may vary.
Educational tools only. FinanceWise is not a lender, broker, bank, or financial advisor.