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How Is Interest Calculated on a Car Loan? Daily vs Monthly Math

ByMd Meraj

Most car loans charge simple interest, which the CFPB describes as interest calculated on your outstanding balance either daily or monthly, so the interest in each payment shrinks as the balance falls. Some loans are instead precomputed, with the total interest fixed at the start. Which one you have, and how your lender counts days, decides how interest is calculated on your car loan. Below is the method in plain terms, a worked example from a Federal Reserve Board page, and what early, extra and late payments do. This is general information, not financial or legal advice, and your loan contract controls.

How Car Loan Interest Works (Simple vs. Amortized)

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The CFPB separates auto loan interest into two methods in its CFPB answer on simple versus precomputed interest (last reviewed January 30, 2024). Simple interest, which it calls far more common, calculates interest based on the outstanding balance of the loan either on a daily or monthly basis. The CFPB also refers to the simple interest formula as an amortizing rate. The amount of interest you pay each month is based on your actual outstanding balance on the day your payment is due, so if you pay more than the minimum, the principal gets smaller.

Precomputed interest works differently. The CFPB says the interest is added to your principal at the beginning of the loan and then split into monthly payments, which allocates more of each payment to interest during the first part of the loan. Making extra payments does not reduce the principal amount or the interest owed. The CFPB calls precomputed interest an uncommon way to calculate auto loan interest and says it benefits the lender if you pay off early, although you may get a refund of some unearned interest.

Simple interest Precomputed interest
When interest is figured On the outstanding balance, daily or monthly Total interest calculated at the start of the loan
Effect of paying extra Principal gets smaller as you pay down the loan Does not reduce the principal amount or interest owed
Paying off early Interest follows the lower balance You may pay more interest overall, with a possible refund of unearned interest
How common (CFPB) Far more common Uncommon

The Federal Reserve Board adds detail on the precomputed side. On a precomputed loan, it says, the lender computes the interest that will accrue on the entire loan amount, that interest becomes part of what you owe, and you should receive a rebate of the portion considered unearned or have it deducted from the payoff amount.

Open lined notebook with a pen on a desk beside a laptop, a coffee cup, a phone and glasses
An open lined notebook and pen on a desk next to a laptop and a coffee cup.

Is Car Loan Interest Calculated Daily or Monthly?

Both appear in the CFPB description: simple interest is calculated on a daily or monthly basis, and the contract you sign determines which. The Federal Reserve Board separates two versions. Under its simple interest method, payments are credited on the due date. Under the daily simple interest method, interest is calculated on the actual balance each day, and payments are credited and the balance reduced on the day the payment is received rather than on the due date.

That timing detail matters when a payment arrives late. The Federal Reserve Board says that if payments are made a few days after the due date each month, the interest paid will be higher than under the simple interest method. In its example, with no extra principal paid and every payment made 5 days after the due date, the total additional interest is $30.38. The same page cautions that laws, lender programs and contracts differ, so your loan may not work like its example.

What daily accrual looks like in numbers

The Federal Reserve Board example uses monthly interest of one twelfth of the annual figure. To see what a per-day view looks like, here is arithmetic only, not a figure from any source, assuming a 365-day year: on the example’s first balance of $18,800 at 9%, $18,800 x 9% / 365 is about $4.64 of interest per day. The Federal Reserve Board page says contracts differ, so check how your own lender counts.

The Exact Formula to Calculate Your Interest

Using the Federal Reserve Board example as the model for a monthly calculation, each payment’s interest is the current balance times the annual rate divided by 12, and the principal portion is the payment minus that interest. The new balance is the old balance minus the principal portion. Repeat for each payment.

  • Interest for the month = balance x annual rate / 12
  • Principal paid = monthly payment – interest for the month
  • New balance = old balance – principal paid

The CFPB adds the order in which payments are applied: a monthly payment is generally applied first to any fees due, such as late fees, then to any interest due, including interest accrued from past payments, and the rest goes to the principal balance. It suggests contacting your lender or servicer, or checking your monthly statement, to confirm how a payment was applied.

Step-by-Step Worked Example

The Federal Reserve Board example of the daily simple interest method uses a loan with an amount financed of $18,800.00, a 48-month term, a 9.00% APR and a monthly payment of $467.84. It states that its first two payments work out as follows, assuming each payment is made exactly on its due date.

  • First payment interest = $18,800 x 9% / 12 = $141.00; principal = $467.84 – $141.00 = $326.84; balance after month 1 = $18,473.16
  • Second payment interest = $18,473.16 x 9% / 12 = $138.55; principal = $467.84 – $138.55 = $329.29; balance after month 2 = $18,143.87
  • Full-term interest, if every payment is made on its due date = ($467.84 x 48) – $18,800 = $3,656.32

Applying the same steps to months 3 through 6 is arithmetic from that formula, rounded to the cent each month, and a lender’s own schedule can differ by cents.

Month Payment Interest Principal Balance after payment
1 (Federal Reserve Board figure) $467.84 $141.00 $326.84 $18,473.16
2 (Federal Reserve Board figure) $467.84 $138.55 $329.29 $18,143.87
3 (arithmetic) $467.84 $136.08 $331.76 $17,812.11
4 (arithmetic) $467.84 $133.59 $334.25 $17,477.86
5 (arithmetic) $467.84 $131.08 $336.76 $17,141.10
6 (arithmetic) $467.84 $128.56 $339.28 $16,801.82

The pattern in the table is the answer to how interest is applied in car finance: interest is highest in month 1 because the balance is highest, and each payment moves slightly more of the $467.84 toward principal.

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Two white arrows painted on gray asphalt, pointing in different directions.

How to Read Your Amortization Schedule

An amortization schedule is the month-by-month version of the table above: each row splits a payment into interest and principal and shows the remaining balance. The CFPB uses the term amortizing rate for simple interest. The CFPB says to contact your lender or servicer, or review your monthly statement, if you want to confirm how payments were applied.

The CFPB explanation of the Truth-in-Lending disclosure for an auto loan (last reviewed March 8, 2024) says lenders and dealers must provide these disclosures before you sign. They include:

  • Annual Percentage Rate (APR): the total cost of credit, including the interest rate and mandatory fees, as a yearly percentage; the CFPB says it is not the same as the interest rate and can be significantly higher with added fees
  • Finance Charge: the total amount of interest and certain fees you will pay over the life of the loan if you make every payment when due
  • Amount Financed: the amount you are borrowing
  • Total of Payments: the sum of all payments at the end of the loan term, including the principal plus finance or interest charges

The CFPB adds that the disclosure also covers the number of payments, late fees and whether you can prepay your loan without a penalty. In the Federal Reserve Board example, the payments total $22,456.32 by arithmetic ($467.84 x 48), which minus the $18,800 amount financed leaves the $3,656.32 of interest.

APR vs. Interest Rate: Which One Drives the Interest?

The CFPB’s answer on the difference between a loan interest rate and the APR says the interest rate is the cost you pay the lender for borrowing, on top of the principal, and that the higher the rate, the more you pay over the life of the loan. The APR is the interest rate plus any additional fees charged by the lender, including origination charges and other fees charged when the loan is made. The CFPB (page last reviewed August 28, 2026) tells borrowers to compare APRs to APRs, not APRs to interest rates, and says that in general a higher credit score means lower rates, though dealers and lenders are not required to offer you the best available rate.

For a deeper look at the two figures, see our interest rate vs. APR guide and our finance charge explainer.

What Extra, Early and Late Payments Do to Interest

The Federal Reserve Board example is useful because it runs the same $18,800, 48-month, 9.00% loan under different methods. The results below are all from that page.

Scenario (Federal Reserve Board example) Result
Daily simple interest, every payment on its due date, no extra principal Total interest $3,656.32
Daily simple interest, extra $1,000 principal at the end of month 1, later payments on time Repaid in 45 months instead of 48; total interest $3,224.84, a saving of $431.48
Daily simple interest, no extra principal, every payment 5 days late Additional interest of $30.38
Constant yield (actuarial) method, extra $1,000 at the end of month 1 No saving of the projected full-term interest, because the interest in each payment is precomputed; the $1,000 is treated as prepayment of the payments due at the end of months 2 and 3

The lesson from the examples is that the loan’s method decides whether an extra payment helps. The CFPB says that if you plan to pay off early you want to make sure the lender uses simple interest, and it suggests asking your lender or servicer to apply more of a payment to principal, after checking your loan documents first. For payoff strategies and loan-length questions, see how to pay off a car loan faster and how long a car loan runs.

Questions to Check in Your Loan Documents

  • Is the interest simple or precomputed (CFPB)?
  • Is simple interest figured daily or monthly, and are payments credited on the due date or the day received (Federal Reserve Board)?
  • What are the APR, finance charge, amount financed and total of payments in the Truth-in-Lending disclosure (CFPB)?
  • Can you prepay without a penalty (listed in the disclosure per the CFPB)?
  • How are payments applied: fees first, then interest, then principal (CFPB)? Can more be applied to principal?

This guide does not cover current auto loan rates, credit score effects, refinancing or state-specific rules; contact your lender or a licensed professional for advice on your own loan.

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Frequently Asked Questions

Is car loan interest calculated daily or monthly?

It depends on the loan contract. The CFPB says simple interest is calculated on the outstanding balance on a daily or monthly basis, and the Federal Reserve Board describes a daily simple interest method that charges interest on the actual balance each day.

Can I pay off a car loan early to save interest?

On a simple interest loan the CFPB says extra payments make the principal smaller; in the Federal Reserve Board example an extra $1,000 in month 1 cut total interest from $3,656.32 to $3,224.84. The CFPB says precomputed loans benefit the lender on early payoff.

What’s the difference between APR and interest rate?

The CFPB says the interest rate is the cost of borrowing, while the APR is the interest rate plus additional fees charged with the loan. It advises comparing APRs to APRs.

How much interest will I pay on an $18,800 car loan?

In the Federal Reserve Board example, an $18,800 loan at a 9.00% APR over 48 months carries $3,656.32 of interest if every payment is on time. That is an illustration, not a quote.

What is precomputed interest on a car loan?

The CFPB says the interest is added to your principal at the beginning of the loan and split into monthly payments, and extra payments do not reduce the principal or interest owed.

Is an 8% car loan rate charged once on the whole loan or every year?

The CFPB describes the APR as a yearly rate. In the Federal Reserve Board example, each month’s interest is the current balance times the annual rate divided by 12.

Bottom Line

Car loan interest is usually simple interest: each period’s interest is the current balance times the annual rate divided into daily or monthly pieces, so it falls as the balance falls. Precomputed loans fix the interest at the start, and extra payments do not reduce it. The loan documents tell you which method and day count apply, and the CFPB and Federal Reserve Board pages cited above explain how to read them. This is general information, not financial advice, and terms vary by lender, contract and state.

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