Calculators & Finance · 3 min read · Sep 2, 2026 · By Finance & Calc Team
Understanding Loan Amortization: Principal vs Interest Explained
How loan amortization schedules work, how extra monthly payments cut down total interest, and formulas behind mortgages and auto loans.
Whether taking out a mortgage, car loan, or business loan, understanding how your monthly payment is split between principal and interest is the key to saving thousands of dollars.
The Amortization Effect
In the early years of a 30-year fixed mortgage, up to 70% of each monthly payment goes toward interest. As the principal balance declines, the interest portion shrinks and the principal portion accelerates.
The Power of Bi-Weekly or Extra Payments
Making just one extra monthly payment per year can shorten a 30-year mortgage by over 4 years and save tens of thousands of dollars in compounding interest.
Use the PolyForge Loan Calculator to simulate custom amortization schedules with extra payment scenarios in real time.