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How is Interest Calculated on an Auto Loan?

December 3rd, 2021 | 9 min. read

How is Interest Calculated on an Auto Loan?


As the Content Specialist and author of the Learning & Guidance Center, Yanna enjoys motivating others by uncovering all that's possible in the world of finance. From financial tips and tricks to ultimate guides and comparison charts, she is obsessed with finding ways to help readers excel in their journey towards financial freedom.

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Lets-Talk-Loans-Circles_Lower-PaymentsWhen applying for an auto loan from a lender (like a bank, credit union, or even a dealership) you're likely to hear about interest.

Interest on an auto loan is essentially the extra fee you pay for using the lender's money to buy a car. Luckily, the interest you'll accrue (and eventually owe) on your loan is spread out over the life of your loan, so you're not required to pay the fee back all at once.

QUICK TIP: You can lower the amount of interest you pay on your loan by paying more than the minimum required monthly loan payment each month. Or avoid interest altogether when repaying the lender in full (if possible).

Some common questions we're asked at the credit union include:

    • How do lenders determine which interest rate to offer?
    • Will my interest rate change over time?
    • How is my interest rate calculated?
    • What's considered a good interest rate on an auto loan?

These are all valid and excellent questions you should ask a lender before applying for an auto loan!

but... here's the frustrating part:

Unfortunately, you won't know your actual interest rate until you're either approved or pre-approved for the loan. In addition, if you're approved for the auto loan, but you're not quite ready to move forward, you could lose that interest rate and auto loan offer after a certain period of time (typically, pre-approvals are good for 30-days).

QUICK TIP: If you're unsure about an auto loan but want an idea of how much money you could be approved for, simply pre-qualify! I talk more about this in The Pros and Cons of Getting Pre-Qualified for an Auto Loan.

In this article, I'll offer some peace of mind and share some factors lenders consider when determining your interest rate so you're better prepared. Ready to learn how interest rates on auto loans work?


Rates-Icon_Greenhow do lenders determine what interest rate to offer on an auto loan?

The interest rate you receive on an auto loan is based on a few factors, including:

  • Credit Score & History - When lenders review your credit score and history, it tells them how many lines of credit you have or if there are negative marks on your credit report. If you have a good credit score (above 700), you can expect to receive a lower interest rate. Your credit score is not the only factor that determines your interest rate, but it is certainly the most important!
QUICK TIP: Request your free credit report every 12-months, so you'll have a good idea what your score is before walking into the dealership or financial institution. Get your credit report for free at
  • The Amount You're Requesting To Borrow – Lenders also look at your previous auto loan amounts and payment history to ensure you can handle the loan. A large down payment on an auto loan reduces how much you’ll owe and helps to secure the loan amount and tells the lender you are serious about paying it back.
  • Debt-to-Income Ratio (DTI) - Lenders determine your borrowing risk based on the percentage of your gross monthly income that pays your monthly debt payments. So, if you have a debt ratio above 50%, you'll have more difficulty finding a reputable lender to finance your loan.
  • The Loan Term (aka the Life of the Loan) – A short loan term could mean larger monthly payments (but less interest paid over the life of the loan) while longer loan terms typically mean lower monthly payments (but more interest paid over the life of the loan). 36- to 72-months is the average loan term.
  • The Vehicle You're Financing  - Typically the older your car is, the higher your interest rate will be simply because it has a lower value.


Thumbs-Up-Icon_Greenwhat’s considered a good interest rate?

Interest rates vary based on the lender, but you can generally expect a lower interest rate when borrowing from a credit union or a bank compared to the dealership. Credit unions specifically offer lower interest rates to their members simply because they're not focused on making profits (psst... credit unions have better approval odds for a loan due to bad or no credit at all. Here’s why.).

Average credit union interest rates:

According to NCUA's comparison of average interest rates between credit unions and banks in 2021 Q1, credit unions average interest rates on car loans are:

    • 2.88% - Used car loan, 48-months
    • 2.77% - Used car loan, 36-months
    • 2.83% - New car loan, 60-months
    • 2.72% - New car loan, 48-months

The comparison chart below is for demonstrative purposes only, but it can help you gain a better understanding of how interest rates are calculated. It includes a range of credit scores to help you grasp a better look at how lenders reach their calculations on interest rates.


Calculator-Icon_Greenhow is my interest rate calculated?

If you're interested in calculating your interest rate, here's what you'll need:

      • An Excel Spreadsheet – This is where you’ll calculate loan details using the formula provided below. Google Sheets are also available on mobile devices. You can download it for free in the Play Store or the App Store.
      • The Desired Loan Amount – This is the amount you're looking to finance.
      • Loan Term – The length (usually listed in months) of your auto loan.
      • The Loan’s Interest Rate - This can be a rate that was offered by your lender, or you can use any of our interest rates on our website (check out our current rate list for available rates). Since the interest rate on a loan is typically noted on an annual basis, we'll be calculating the Annual Percentage Rate (APR).
      • Additional Fees – This could include an origination fee (a fee charged by the lender), GAP insurance, title transfer fee, fees for new tags, or property / highway tax. Also, consider dealer fees which could include a wide range of charges if you are financing through the dealership.

Feel free to use the credit scores on the comparison chart above to help you get a sense of the interest rate you could receive when borrowing from a lender and calculating your estimated APR.


ready to start calculating?

Let’s say:

    • You’re looking to finance a vehicle for $15,000 ($14,500, plus $500 in fees)
    • Your loan term is 72-months
    • You have an interest rate of 8.99% APR
how To determine your monthly payment:

On your spreadsheet  (i.e. Google Sheet or Excel)  use the following formula to begin calculating your monthly payment:

=PMT (interest rate as a decimal/12, number of months in the term, loan amount and with fees)  

      • Plugin the information   =PMT(0.0899/12, 72, 15000)
      • Your spreadsheet should calculate the monthly payment as -$270.31


how to calculate your estimated interest rate:

On your spreadsheet (i.e., Google Sheet or Excel) you’ll use the following formula to help you calculate your estimated interest rate:

=RATE (number of months in loan term, estimated monthly payment as a negative, value of loan)*12  

      • Plugin the information   =RATE(72,-270.31, 15000)*12
      • Your spreadsheet should calculate the estimated APR at approximately 0.089901858 (or 8.99% in a percentage format)  


If you're not a fan of spreadsheets, there are plenty of interest rate calculators online you can check out instead. includes a detailed breakdown of terms as well as a chart and graph showing the principal and interest breakdown.

You can also use Charlotte Metro's loan payment calculator to find your monthly payments, total interest, and total loan cost. It helps to know your loan information, such as the loan amount, loan term (months), interest rate, and payment frequency.


Listing-Icons_Greenhere's what’s next:

Remember, interest will most likely be involved when you finance a vehicle. Feel free to use the options above (interest rate formula, Charlotte Metro's calculators, or visit ) to calculate your interest. And don't forget to grab your free credit reports from once every 12 months.

  1. Remember, multiple factors are considered when determining an auto loan, such as the applicant's credit score, debt-to-income ratio, and loan term.

  2. When searching fees and pricing for new and used cars, head to Kelley Blue Book. It’s a reliable resource many lenders use when prospective borrowers inquire about auto loans. You can also compare cars and find vehicles for sale.  

Now that you understand what goes into calculating interest on an auto loan, you'll be more confident can talk to your preferred lender more confidently when discussing rates.