Auto Loan Amortization: What It Is and How to Read the Schedule

What Is Amortization and How Does It Apply to Car Loans?

Amortization describes the process of gradually paying off an auto loan. Each monthly payment is split between the principal—the amount you borrowed—and the interest—the cost of borrowing that money. Over time, the proportion of each payment that goes toward principal increases while the interest portion decreases.

In the early months of a typical auto loan, most of your payment goes toward interest. As you continue making payments, the balance shrinks, so the interest charged on that balance is lower, and more of your payment applies to the principal. This is true for what are called simple interest auto loans, where interest is calculated based on the outstanding balance each month.

Sources: Consumer Financial Protection Bureau

The Parts of an Amortization Schedule: Payment, Principal, Interest, Balance

An amortization schedule is simply a table that shows the breakdown of each loan payment. For a typical auto loan, the schedule includes the following for each payment period:

• Payment number – the sequential number of the payment
• Payment amount – the total monthly payment, which stays the same for a fixed-rate loan
• Interest – the portion of that payment that goes toward interest
• Principal – the portion that goes toward reducing the loan balance
• Remaining balance – the amount you still owe after that payment

Sources: Consumer Financial Protection Bureau, Chase Bank, TransUnion

How to Read an Amortization Schedule

Reading an amortization schedule is largely a matter of tracking how the principal and interest portions change over time. In the first payment, the interest is highest because the outstanding balance is large. By the final payment, almost the entire payment goes toward principal and only a tiny amount is interest.

You can use the schedule to see how much total interest you’ll pay over the life of the loan, and to determine your outstanding balance at any point—useful if you’re considering paying off the loan early. It also helps you understand the effect of choosing a longer term: lower monthly payments come with higher total interest.

Sources: Consumer Financial Protection Bureau, RateGenius, TransUnion

Creating Your Own Schedule: Formula and Spreadsheet Example

If you want to create an amortization schedule yourself, you can use the standard calculation for a fixed-rate amortized loan. The formula for the monthly payment M is:

M = P × [r(1 + r)^n] / [(1 + r)^n - 1]

In this formula, P is the principal (loan amount), r is the monthly interest rate (annual rate divided by 12), and n is the total number of payments (loan term in months). This formula is commonly used by lenders and financial educators.

Here is a concrete example. Suppose you borrow $20,000 at an annual percentage rate (APR) of 6% for a 60-month term. The monthly interest rate r is 0.06/12 = 0.005, and n is 60. Plugging these into the formula gives a monthly payment of approximately $386.66. (Note: this example is illustrative; actual payments may vary based on your specific rate and terms.)

You can then build the first few rows of the schedule manually. For the first month, the interest on the starting balance is 0.005 × 20,000 = $100.00. Subtract that from the monthly payment to get the principal portion: 386.66 - 100.00 = $286.66. The new balance is 20,000 - 286.66 = $19,713.34. For the second month, the interest is 0.005 × 19,713.34 = $98.57, the principal portion is 386.66 - 98.57 = $288.09, and the new balance is 19,713.34 - 288.09 = $19,425.25. By the final, 60th payment, the balance reaches zero. Here are the first two rows and the final row of the schedule:

Payment 1: $386.66 payment, $100.00 interest, $286.66 principal, $19,713.34 balance

Payment 2: $386.66 payment, $98.57 interest, $288.09 principal, $19,425.25 balance

Payment 60: $386.66 payment, $2.00 interest, $384.66 principal, $0 balance

To create the full schedule yourself, you can set up a spreadsheet. In a spreadsheet, you could use formulas to calculate each month's interest and principal based on the previous balance. For instance, if you put the starting balance in cell B2 and the monthly rate in cell C2, you could use formulas like =B2*$C$2 for interest, and =$E$2 - that interest for the principal, with the new balance calculated as the previous balance minus the principal. Many spreadsheet applications also have built-in functions like PPMT and IPMT to calculate principal and interest directly. This allows you to quickly model different loan amounts, rates, and terms.

Sources: Consumer Financial Protection Bureau, Pima Community College, Six Minutes. Smarter.

The Benefits of Understanding Amortization

Whether you obtain a schedule from your lender or create your own with a spreadsheet, you can use the information to decide how much to borrow, what term to choose, and whether making extra payments makes sense for your situation.

Sources: Consumer Financial Protection Bureau, RateGenius, Pima Community College, TransUnion

How Extra Payments Alter the Schedule

Making extra payments toward the principal can have a significant impact on your loan. By reducing the principal balance faster, the interest charged on each subsequent payment is lower, which means more of your regular payment goes toward principal and less toward interest. This can shorten the loan term and reduce the total interest you pay.

It’s important to note that this benefit applies to simple interest auto loans. If your loan uses precomputed interest, the interest is calculated at the start and spread across all payments, so extra payments may not reduce the total interest owed. Check your loan documents or ask your lender about how extra payments are applied.

Sources: Consumer Financial Protection Bureau, Six Minutes. Smarter.