How Extra Loan Payments Reduce Interest

Last updated: August 2026

How Loan Amortization Works

Each monthly loan payment is split between interest and principal. Early in the loan, most of your payment goes toward interest. Over time, the interest portion shrinks and more goes to principal. Making extra payments toward principal accelerates this process — and those extra dollars go 100% toward reducing your balance.

Example: $25,000 Car Loan at 7.5%

• Regular $500/month: Payoff in approximately 61 months (5 years, 1 month). Total interest: ~$5,069.
• $500 + $100 extra per month: Payoff in approximately 49 months (4 years, 1 month). Total interest: ~$4,051. Savings: ~$1,018 and 12 months.

Even a modest extra payment compounds: try it yourself with the Loan Payoff Calculator.

Should Extra Payments Go to Principal?

Yes. When you make an extra payment, it should be applied to the principal balance unless you instruct otherwise. Some lenders require you to explicitly mark extra payments as "principal-only." If you don't, they may treat it as an advance on your next regular payment, which doesn't save you interest.

Watch for Prepayment Penalties

Some loans — particularly mortgages and auto loans — may charge a prepayment penalty if you pay off the loan early. Check your loan agreement before making large extra payments. Federal law restricts prepayment penalties on many mortgage types, but they still exist on some loans.

One-Time vs. Monthly Extra Payments

• Monthly extra: Adding a consistent amount each month steadily reduces the term.
• Lump sum: A one-time payment reduces the balance immediately, shortening all remaining payments.
• Biweekly payments: Paying half your monthly amount every two weeks results in 26 half-payments (13 full payments) per year instead of 12, effectively making one extra payment annually.

Source: CFPB. For informational purposes only.