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An auto loan calculator computes the monthly payment on a car purchase by accounting for the vehicle price, trade-in equity or negative equity rollover, down payment, sales tax, and the lender's APR. CalcForge's calculator also supports extra monthly payments for early payoff planning and shows the full amortization schedule.
Estimate monthly payments for a car purchase, including trade-in equity, negative equity rollover, down payment, and sales tax.
Estimated Monthly Payment
$439.26
for 60 months
Financed Amount
$22,450.00
Price + tax - trade-in - down
Net Trade Equity
$12,000.00
Applied toward new purchase
Total Interest
$3,905.60
14.8% of total cost
Total Cost
$26,355.60
Principal + interest
This is an estimate for informational purposes only. Actual terms vary by lender, state, and credit profile. Always review your loan agreement carefully before signing.
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When you trade in a vehicle, the net equity (trade-in value minus any remaining loan balance) is applied toward the new purchase. If you owe less than the car is worth, the equity reduces the amount you need to finance. Sales tax is then calculated on the vehicle price and added to the loan. The financed amount is the total after subtracting net trade equity and down payment from the price-plus-tax total.
Worked example (computed by engine): A $35,000.00 vehicle with a $12,000.00 trade-in (owned outright), $3,000.00 down, and 7% sales tax at 6.5% APR for 60 months. The sales tax adds $2,450.00, net trade equity is $12,000.00, and the financed amount is $22,450.00. The monthly payment is $439.26, total interest is $3,905.60, and total cost is $26,355.60.
Paying more than the required amount each month directs the surplus toward principal. Because auto loan interest is computed on the declining balance, reducing the balance ahead of schedule means less interest accrues in every subsequent month. The result is a shorter loan term and lower total interest, even though the required monthly payment stays the same.
Worked example (computed by engine): A $30,000.00 vehicle with $5,000.00 down and 6% sales tax at 7% APR for 60 months finances $26,800.00. The base monthly payment is $530.67 and total interest is $5,040.35. Adding $75.00 per month from month 1 shortens the loan by 8 months and saves $750.11 in interest, bringing the total cost from $31,840.35 to $31,090.24.
Negative equity on a trade-in is one of the costliest aspects of auto financing. If your current car is worth less than the loan balance, the dealer rolls the shortfall into the new loan. You are now paying interest on old debt in addition to the new vehicle. The calculator handles this automatically: enter the trade-in value and the amount still owed, and it adds the difference to the financed amount.
Worked example with negative equity (computed by engine): A $32,000.00 vehicle with a $10,000.00 trade-in that still has $14,000.00 owed. Net trade equity is -$4,000.00, meaning $4,000.00 of old debt rolls into the new loan. With $2,000.00 down and 8% sales tax at 6.5% APR for 72 months, the financed amount is $36,560.00. The monthly payment is $614.57 and total interest is $7,689.13.
Without the negative equity, the same deal would finance $22,560.00 and carry $4,744.74 in interest. The $4,000.00 rollover adds $2,944.39 in extra interest over the 72-month term. Adding $100.00 per month in extra payments shortens this loan by 11 months and saves $1,320.33 in interest.
Negative Equity Warning
Sales tax on a vehicle purchase is determined by the state, county, and sometimes the city where the car is registered. The rate you pay can vary by several percentage points depending on where you live, and some jurisdictions add additional fees on top of the base rate.
Beyond the rate itself, states differ on what the tax applies to. Some states tax the full purchase price. Others allow you to deduct the trade-in value and tax only the net amount. This distinction materially changes the financed amount. On a $35,000.00 vehicle with a $12,000.00 trade-in and 7% tax, taxing the full price adds $2,450.00. Taxing only the net would add $1,610.00, a difference of $840.00.
Because these rules are set at the state level and change over time, the calculator does not include a state rate lookup. Enter your actual combined rate in the Sales Tax Rate field. If your state exempts trade-in value from taxation, calculate the effective rate that produces the correct tax amount on the full purchase price, and enter that instead.
A 72-month (6-year) term extends the repayment window to six years. Extending the term from 36 months to 84 months lowers each monthly payment but raises the total interest paid, and it extends the window during which the borrower owes more than the car is worth. The table below shows how the term affects a $35,000.00 loan at 6.5% APR.
| Term | Monthly Payment | Total Interest | Total Cost |
|---|---|---|---|
| 36 months | $1,072.72 | $3,617.73 | $38,617.73 |
| 48 months | $830.02 | $4,841.14 | $39,841.14 |
| 60 months | $684.82 | $6,088.86 | $41,088.86 |
| 72 months | $588.35 | $7,360.98 | $42,360.98 |
| 84 months | $519.73 | $8,657.35 | $43,657.35 |
Moving from 36 months to 84 months drops the payment from $1,072.72 to $519.73, but total interest rises from $3,617.73 to $8,657.35. The longer term also extends the period during which the loan balance exceeds the vehicle's resale value, which matters if you sell or total the car before the loan is paid off.
Compare auto loan costs against other borrowing products with our Personal Loan Calculator, Boat, RV & Motorcycle Loan Calculator, or Business Loan Calculator, or browse all tools on the Loan Calculators hub.