Auto Loan Amortization Schedule: Calculate Each Payment

Calculate an auto loan amortization schedule by entering the amount financed, APR, and loan term. The calculator estimates the fixed monthly payment and total interest; an amortization schedule then shows how each payment is divided between interest and principal and how the balance declines.

Formula

For a fixed-rate loan with equal monthly payments, first calculate the monthly rate and number of payments, then use the level-payment formula:

• r = APR ÷ 1,200, the monthly interest rate as a decimal.
• n = loan term in years × 12, the number of monthly payments.
• P = amount financed in dollars.
• M = monthly payment in dollars: P × r ÷ [1 − (1 + r)⁻ⁿ].

The calculator displays M rounded to cents. Its total-interest estimate is the rounded monthly payment multiplied by the number of payments, minus the original principal: M × n − P. That convention makes the displayed total match the payment shown; a lender’s final payment may differ slightly because of rounding or payment dates.

To build the schedule, calculate each month in sequence. Interest for a period is the opening balance multiplied by r. Principal paid is M minus that period’s interest. The closing balance is the opening balance minus principal paid. The next period’s opening balance is the previous period’s closing balance. In symbols, for payment k: interest_k = balance_k−1 × r; principal_k = M − interest_k; balance_k = balance_k−1 − principal_k.

Worked Example

Using the calculator’s default inputs, the amount financed is $20,000, APR is 8%, and the term is 5 years.

1. Monthly rate: r = 8 ÷ 1,200 = 0.0066667.
2. Number of payments: n = 5 × 12 = 60.
3. Monthly payment: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰] = $405.53 when rounded to cents.
4. Total paid using the rounded payment: $405.53 × 60 = $24,331.80.
5. Estimated total interest: $24,331.80 − $20,000 = $4,331.80.

For the first month, interest is $20,000 × 0.0066667, or about $133.33. The principal portion is about $405.53 − $133.33 = $272.20, leaving a balance of about $19,727.80. In month two, interest is calculated on that lower balance, so slightly more of the same payment goes toward principal.

Assumptions

• The APR stays fixed for the full term.
• Payments are equal, monthly, and made at the end of each monthly period.
• Interest compounds monthly using APR ÷ 12.
• The estimate excludes fees, taxes, insurance, optional products, and other charges unless they are included in the amount financed.

How to Read an Auto Loan Schedule

A full schedule normally has one row per payment, with columns for the payment number or date, opening balance, payment, interest, principal, and closing balance. Early in a conventional amortizing loan, the balance is relatively high, so the interest share of a level payment is larger. As the balance falls, the interest charge generally declines and the principal share rises. The payment itself stays level under the assumptions above.

The final row should bring the balance to zero, subject to rounding. A schedule calculated with full precision may show a tiny residual balance if each row is rounded to cents. If payments are rounded period by period, the last payment may need a small adjustment. For the lender’s actual due dates, payoff amount, and final payment, use its account statement or loan disclosure rather than treating this estimate as a payoff quote.

What Amount and APR Should You Enter?

Use the amount financed, not automatically the vehicle’s advertised price or the amount of a down payment. The financed amount can reflect a down payment or trade-in and may include items added to the contract. Enter the amount actually borrowed as stated in the lender’s documents. If the contract gives a financed balance that already includes charges, do not add those charges a second time.

Enter the APR as a percentage per year: for example, 8 means 8%, not 0.08. The calculator converts it to a monthly rate by dividing by 1,200. The default is an example only; obtain the actual APR, financed amount, and term from the lender’s written figures. A quoted interest rate and an APR may not be identical when certain costs are reflected in APR, so use the figure that corresponds to the calculation you intend to estimate.

Extra Payments and Early Payoff

The schedule above assumes the required payment only. An extra payment directed to principal can reduce the balance, which generally changes the interest that accrues later. However, the effect depends on how the lender applies extra funds, payment timing, contract terms, and whether the payment is treated as principal reduction or as an advance toward a future payment. This calculator does not model those details, so it cannot provide an exact early-payoff date or savings estimate.

Likewise, making a payment early or late can change the number of days interest accrues under the loan’s actual method. A monthly approximation is useful for understanding amortization, but it is not a substitute for the lender’s transaction history or payoff calculation.

Common Calculation Mistakes and Limits

• Mixing percentage formats: Enter APR as a percent, such as 8, rather than a decimal, such as 0.08.
• Using the wrong principal: The calculation needs the amount financed, not the vehicle price before down payment or trade-in.
• Rounding too early: Rounding the monthly rate or every intermediate value can create small differences. The calculator rounds the payment to cents and uses that rounded payment for total interest.
• Assuming every contract is a standard loan: Variable rates, irregular payment schedules, balloon payments, deferred payments, and daily-interest methods do not follow this simple model exactly.

The formula also assumes the monthly payment is sufficient to repay principal and interest over the entered term. It does not determine whether a loan is available, include fees not financed, or calculate a lender-specific payoff. Use the lender’s disclosed terms for contractual figures.

Frequently Asked Questions

How do I calculate the interest in each car payment?
Multiply the balance at the start of the period by the monthly rate (APR ÷ 1,200). Subtract that interest from the payment to estimate the amount applied to principal.

Why does more of my payment go to interest at the beginning?
Interest is calculated on the outstanding balance. The balance is largest at the beginning, so the interest portion is larger; as principal is repaid, interest generally falls.

Does an amortization schedule include a down payment?
Not as a separate payment. A down payment affects the schedule only by reducing the amount financed. Enter the balance borrowed, not the down payment itself.

Why is my lender’s payment or interest total different?
Differences can result from the actual financed amount, APR, payment dates, fees included in the contract, day-count method, rounding, or a final-payment adjustment. Compare the schedule inputs with the lender’s disclosure.

Can I use this schedule to find an exact payoff amount?
No. The estimate uses regular monthly periods and excludes lender-specific accrued interest, transaction timing, and other contract details. Request a payoff figure from the lender for an exact amount.

This result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Auto Loan Calculator With Trade-In and Amount Owed (Negative Equity)
• Car Loan Calculator With Down Payment: Monthly Car Payment

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2