How Loan Amortization Works, Using a Car Loan Example
A car loan payment looks like one fixed number every month. Underneath, it is two different things: interest, which is the cost of borrowing, and principal, which actually reduces what you owe. The Consumer Financial Protection Bureau describes amortization as the process of gradually paying off a loan, where a portion of each monthly payment goes to the principal and a portion goes to the finance charge. How that split changes over time explains why a longer loan costs more and why early payoff behaves the way it does.
1. The example loan
The numbers below assume a $28,000 amount financed at a 7.0% annual interest rate with fixed monthly payments and no fees added. These are illustrative assumptions. Your own rate depends on your credit, the lender, the vehicle, and the term.
| Term | Monthly payment | Total interest over the loan |
|---|---|---|
| 60 months | $554.43 | $5,266 |
| 72 months | $477.37 | $6,371 |
Stretching the loan by a year lowers the payment by about $77 a month but adds roughly $1,105 in interest. The CFPB makes the same general point: a shorter term reduces your total loan cost, while a longer one can reduce your monthly payment but you pay more interest over the life of the loan.
2. Month one, taken apart
Interest for a month is the outstanding balance times the monthly rate (7.0% divided by 12).
- First-month interest: $28,000 x 0.5833% = $163.33
- On the 60-month loan, the rest of the $554.43 payment, $391.10, goes to principal.
As the balance shrinks, the interest portion shrinks with it, so a growing share of the same fixed payment goes to principal. In the final months, almost the whole payment is principal.
3. Where you stand after one year
Because early payments are interest-heavy, the balance falls more slowly at first than many borrowers expect.
| After 12 payments | 60-month loan | 72-month loan |
|---|---|---|
| Remaining balance | $23,153 | $24,108 |
| Principal paid so far | $4,847 | $3,892 |
On the 72-month loan, after three years of payments you would still owe about $15,460. That matters because cars lose value over time. The CFPB defines negative equity as owing more on the vehicle than it is worth, and notes that a longer loan puts you at greater risk of it. If you need to sell or trade in while upside down, the difference has to be paid off or rolled into the next loan.
4. The order your payment is applied
The CFPB's key terms page explains that, generally, any payment made on an auto loan is applied first to fees that are due, such as late fees, then to interest due, including past-due interest, and only then to the principal balance. A late payment therefore does double damage: the fee is taken first, and less of your money reaches principal.
5. What your loan paperwork shows
Federal Truth in Lending rules require closed-end loan disclosures to show specific items, including:
- the amount financed, the amount of credit provided to you or on your behalf;
- the finance charge, described as the dollar amount the credit will cost you;
- the payment schedule, with the number, amounts, and timing of payments; and
- the total of payments, the amount you will have paid after all scheduled payments.
Those four numbers let you check the math above against any real offer. The finance charge on the disclosure is the lender's own total-interest figure, plus any finance-related fees.
6. How extra payments change the picture
Since interest each month is calculated on the remaining balance, any extra money that goes to principal lowers every future interest charge. Paying extra early in the loan has the largest effect, because it removes balance that would otherwise have been charged interest for years. Before you do this, confirm with the lender that extra amounts are applied to principal and check your contract for any prepayment terms.
7. Key takeaways
- Each payment on an amortizing loan is split between interest and principal, and the principal share grows over time.
- A $28,000 loan at 7.0% costs about $5,266 in interest over 60 months and $6,371 over 72 months.
- In month one, $163.33 of the payment is interest; on the 60-month loan, $391.10 reduces the balance.
- After 12 payments, the 72-month loan still has about $24,108 owed, which raises the risk of negative equity.
- Payments generally go to fees first, then interest, then principal, so late fees slow down your payoff.