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Finance Calc Kit
Auto finance

Auto Loan Calculator

Calculate your monthly car loan payment, total interest, and comprehensive amortization schedule with optional sales tax and trade-in value.

Vehicle & Loan Details

$
%
mo

Down Payment & Trade-in

$
$
$

Taxes, Fees & Payoff

%
$
$

Monthly Payment

$641.97

60 months at 6.5% APR

Amount Financed
$32,810.00
Total Interest
$5,707.92
Sales Tax & Fees
$2,810.00
Total Vehicle Cost
$43,517.92

Loan repayment breakdown

  • Principal financed$32,810.0085.2%
  • Total interest$5,707.9214.8%

Loan term comparison

Compare monthly payments and total interest across different financing terms.

TermMonthly PaymentTotal InterestTotal Vehicle CostAction
24 mo (2 yr)
$1,461.56$2,267.50$40,077.50
36 mo (3 yr)
$1,005.59$3,391.38$41,201.38
48 mo (4 yr)
$778.09$4,538.21$42,348.21
60 mo (5 yr)Selected
$641.97$5,707.92$43,517.92Active
72 mo (6 yr)
$551.53$6,900.43$44,710.43
84 mo (7 yr)
$487.21$8,115.64$45,925.64

How your car loan payment is calculated

Four steps from vehicle price and trade-in to monthly installments and total loan interest.

  1. 1. Calculate net trade-in equity and sales tax

    Net Trade-In=Trade-In Value−Amount Owed\text{Net Trade-In} = \text{Trade-In Value} - \text{Amount Owed}

    Trade-in equity is $2,000.00. Sales tax of 7.0% applies to the taxable base ($33,000.00), yielding $2,310.00.

  2. 2. Determine total amount financed (principal)

    P=Price+Tax+Fees−Down Payment−Net Trade-InP = \text{Price} + \text{Tax} + \text{Fees} - \text{Down Payment} - \text{Net Trade-In}

    Total financed principal P is $32,810.00. Taxes and dealer fees are rolled into the loan balance.

  3. 3. Calculate monthly payment with amortization formula

    Monthly Payment=P×r(1+r)n(1+r)n−1\text{Monthly Payment} = P \times \frac{r(1 + r)^{n}}{(1 + r)^{n} - 1}

    With monthly rate r = 0.005417 and n = 60 months, the standard monthly installment is $641.97.

  4. 4. Compute total interest and total ownership cost

    Total Interest=(Monthly Payment×n)−P\text{Total Interest} = (\text{Monthly Payment} \times n) - P

    Over 60 months, total scheduled payments equal $38,517.92, containing $5,707.92 in total finance charges. Total vehicle cost is $43,517.92.

Amortization Schedule

Year-by-year payment schedule. Expand any year to view monthly principal and interest breakdowns.

PeriodPaymentPrincipalInterestBalance
$7,703.58$5,739.93$1,963.65$27,070.07
$7,703.58$6,124.35$1,579.24$20,945.72
$7,703.58$6,534.51$1,169.08$14,411.21
$7,703.58$6,972.14$731.45$7,439.07
$7,703.58$7,439.07$264.51$0.00
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How auto loans and car financing work

An auto loan is a secured installment loan used to purchase a motor vehicle. The lender provides upfront capital to cover the vehicle price, applicable state sales taxes, and dealership documentation fees. In return, you agree to repay the borrowed principal along with interest in fixed monthly payments over a predetermined term, typically ranging from 24 to 84 months.

Because the vehicle itself serves as collateral for the loan, interest rates on car loans are typically lower than unsecured personal debt. If you are comparing installment financing against vehicle leasing, examine our auto lease calculator to see how depreciation-only lease payments compare with building full vehicle equity. For recreational watercraft financing, check our boat loan calculator, or for general installment schedules explore our EMI calculator.

Key components of a car loan

Calculating your true car loan cost requires accounting for several interacting financial factors:

  • Vehicle Purchase Price: The agreed-upon sale price of the new or used vehicle before taxes and fees.
  • Cash Down Payment: Upfront cash contributed at the time of purchase, which directly reduces the principal amount you need to borrow.
  • Trade-in Value and Net Equity: The market valuation of your existing car credited toward the new purchase. If you still owe money on your old vehicle, your net equity equals the trade-in offer minus the remaining loan payoff balance.
  • Sales Tax and Trade-in Tax Credits: In most US states and jurisdictions, sales tax is assessed only on the net purchase price after deducting the trade-in allowance (Taxable Base=Price−Trade-In\text{Taxable Base} = \text{Price} - \text{Trade-In}).
  • Dealer and Documentation Fees: State title, registration, licensing, and dealer processing fees, which can either be paid upfront in cash or rolled directly into the financed loan amount.
  • Annual Percentage Rate (APR): The yearly cost of credit expressed as a percentage rate. To evaluate how APR compares against compounding yields on other financial products, use our APR calculator.
  • Loan Term: The duration of the loan in months. While longer loan terms reduce your monthly payment, they increase the total interest paid over the life of the loan.

Mathematical formulas for auto loan calculations

Car loan payments follow the standard reducing-balance amortization schedule.

1. Determining the financed principal

When sales tax and dealer fees are rolled into the loan, the financed principal PP is calculated as:

P=Vehicle Price+Sales Tax+Fees−Down Payment−(Trade-In−Amount Owed)P = \text{Vehicle Price} + \text{Sales Tax} + \text{Fees} - \text{Down Payment} - (\text{Trade-In} - \text{Amount Owed})

2. Monthly installment payment

The fixed monthly payment MM is determined by applying the periodic interest rate r=APR/12r = \text{APR} / 12 across the total number of monthly periods nn:

M=P×r(1+r)n(1+r)n−1M = P \times \frac{r(1 + r)^n}{(1 + r)^n - 1}

If the interest rate is zero percent (such as a 0% APR manufacturer promotional financing offer), the formula simplifies directly to M=P/nM = P / n. You can inspect comprehensive amortization curves and payment balances over time in our amortization calculator.

3. Total interest and lifetime cost

The cumulative finance charges over the loan term are calculated by subtracting the financed principal from total monthly payments:

Total Interest=(M×n)−P\text{Total Interest} = (M \times n) - P

Published worked example

Consider a standard auto loan with the following parameters:

  • Vehicle Purchase Price: $30,000
  • Annual Interest Rate: 6.00% APR
  • Loan Term: 60 months (5 years)
  • Cash Down Payment: $3,000
  • Trade-in Allowance: $2,000 (with $0 balance owed)
  • Sales Tax Rate: 7.00% (tax applies to $30,000 - $2,000 = $28,000 taxable base)
  • Dealer and Documentation Fees: $400
  • Financing Option: Taxes and fees rolled into loan

The step-by-step calculations proceed as follows:

  1. Sales Tax: $28,000 * 0.07 = $1,960.00.
  2. Financed Principal: $30,000 + $1,960 + $400 - $3,000 - $2,000 = $27,360.00.
  3. Monthly Interest Rate: 0.06 / 12 = 0.005.
  4. Monthly Payment: $27,360 * [0.005 * (1.005)^60] / [(1.005)^60 - 1] = $528.95 per month.
  5. Total Scheduled Payments: $528.95 * 60 = $31,736.81.
  6. Total Interest Paid: $31,736.81 - $27,360.00 = $4,376.81.
  7. Total Out-of-Pocket Vehicle Cost: $3,000 (down) + $2,000 (trade-in) + $31,736.81 (payments) = $36,736.81.

For detailed loan scheduling scenarios with irregular lump sums, check our advanced loan calculator.

Choosing the right auto loan term

Selecting the ideal loan duration requires balancing monthly cash flow against long-term interest expense:

Shorter terms (36 to 48 months)

  • Substantially lower total interest expense over the life of the loan.
  • Lenders frequently offer lower APRs on shorter maturities.
  • Builds vehicle equity quickly, reducing the risk of being underwater.
  • Requires higher monthly cash flow commitments.

Longer terms (72 to 84 months)

  • Lower monthly payments provide greater monthly budget flexibility.
  • Significantly higher lifetime interest costs.
  • High risk of negative equity (owing more than the car is worth for years).
  • May outlast the vehicle manufacturer warranty coverage.

Frequently asked questions

What is negative equity on a car trade-in?
Negative equity occurs when you owe more on your existing auto loan than the dealer offers for the trade-in vehicle (also known as being "upside down" or "underwater"). If you trade in a car worth $10,000 while owing $12,000, the remaining $2,000 shortfall is typically added to your new vehicle loan balance.
How does a trade-in affect auto sales tax?
In most US states, trade-in value provides a sales tax credit. The state sales tax is calculated only on the difference between the new vehicle purchase price and the trade-in value. For example, buying a $30,000 car with a $5,000 trade-in means you only pay sales tax on $25,000.
Should I finance sales tax and fees or pay them upfront?
Paying sales tax, registration, and dealer fees upfront in cash is generally recommended. Rolling these fees into your loan increases your financed principal and total interest cost, and increases the likelihood of starting your loan with negative equity.
Can I pay off my auto loan early to save on interest?
Yes. Most standard auto loans use simple interest without prepayment penalties. Making extra monthly principal payments directly reduces your outstanding balance, shortening your repayment timeline and lowering total interest charges.
What credit score is needed for the best auto loan interest rates?
Borrowers with super-prime credit scores (780 and above) generally qualify for the lowest advertised interest rates and manufacturer incentive financing. Prime borrowers (660 to 779) receive competitive rates, while non-prime and subprime borrowers face higher APRs and stricter loan terms.
What is GAP insurance and do I need it?
Guaranteed Asset Protection (GAP) insurance covers the financial gap between what your auto insurance pays if your vehicle is totaled or stolen (actual cash value) and what you still owe on your loan. GAP insurance is strongly recommended if you make a small down payment (under 20%) or choose a loan term of 60 months or longer.

Resources and references

The formulas and methods in this calculator were checked against these independent sources.