Estimate your monthly auto loan payment and the full cost of buying a car, including sales tax, fees, rebates, down payment, and trade-in (including negative equity). You will also see what you pay upfront vs what you finance, plus how extra monthly payments can shorten payoff time.
Advanced options
How to use this calculator
- Enter the Vehicle price (the price before tax and fees).
- Enter the Interest rate (APR) and your Loan term in months (example: 60 months).
- Enter your Cash down payment (money you will pay upfront).
- Enter your Sales tax rate for your area.
- Open Advanced options and add a Trade-in value and any Amount you still owe on trade-in to see if negative equity increases the new loan.
- Add Cash rebate and Other fees (doc, title, registration estimate) from your buyer paperwork.
- Choose whether to Roll fees into the loan and whether to Roll sales tax into the loan (rolling in means you borrow it; not rolling in means you pay it upfront).
- Pick How to apply sales tax (common methods differ by state and by what the dealer taxes).
- If you want to pay the loan off faster, enter an Extra payment each month.
- Click Calculate and review the results: monthly payment, amount financed, upfront cash due, total interest, and payoff time.
Definitions
APR (annual percentage rate): The yearly cost to borrow money, shown as a percent. This calculator converts APR to a monthly rate for the payment math. [3]
Amortizing loan: A loan you pay down with regular payments. Each payment covers interest first, then the rest goes to principal (the amount you borrowed). [2]
Amount financed: The starting loan balance after adding items you roll into the loan and subtracting items that reduce what you need to borrow.
Down payment: Cash you pay upfront that reduces how much you borrow.
Trade-in value: The credit you get for your old car.
Trade-in owed (payoff): What you still owe on your old car loan. If this is bigger than the trade-in value, the difference is negative equity.
Negative equity: When you owe more on your trade-in than it is worth. It can increase your new loan balance.
Sales tax rate: The percent used to estimate sales tax on the purchase. Rules on what gets taxed vary by location.
Upfront cash due: What you pay out of pocket at purchase in this estimate (down payment plus any tax or fees you chose not to finance).
Methodology
What gets added vs subtracted
This calculator separates the deal into (1) purchase items (vehicle price, estimated sales tax, and fees), (2) credits (rebates and trade-in), and (3) financing cost (interest). It also splits what you pay upfront from what you choose to roll into the loan.
Step 1: Estimate taxable amount and sales tax
You choose a tax method because different states and dealer paperwork can tax different bases. The calculator sets a taxable base using your selection, then applies a floor of 0 so it cannot go negative: taxable_amount = max(0, method_base). Sales tax is then estimated as sales_tax_amount = taxable_amount * (sales_tax_rate/100).
Step 2: Handle trade-in and negative equity
The trade-in effect is net_trade_credit = trade_in_value - trade_in_owed. If this number is negative, that is negative equity and it increases the new loan balance. The calculator reports negative_equity_added as max(0, trade_in_owed - trade_in_value).
Step 3: Compute amount financed and upfront cash due
Fees and sales tax can be either financed or paid upfront. financed_fees is fees_total if you choose to roll fees into the loan, otherwise 0. financed_tax is sales_tax_amount if you choose to roll tax into the loan, otherwise 0. The starting balance is amount_financed = vehicle_price + financed_fees + financed_tax - down_payment - net_trade_credit - rebate_cash. Upfront cash due is upfront_cash_due = down_payment + upfront_fees + upfront_tax, where upfront_fees is fees_total only if you do not roll fees in, and upfront_tax is sales_tax_amount only if you do not roll tax in.
Step 4: Monthly payment from APR
The monthly interest rate is monthly_rate = (apr/100)/12. The monthly payment for a fixed-rate amortizing loan is: if monthly_rate = 0, monthly_payment = amount_financed / loan_term_months; otherwise monthly_payment = amount_financed * monthly_rate / (1 - (1 + monthly_rate)^(-loan_term_months)). This is standard amortizing loan math. [2][3]
Step 5: Interest totals and extra payment payoff
Without extra payments, total_of_payments = monthly_payment * loan_term_months and total_interest_paid = total_of_payments - amount_financed (with 0 interest when APR is 0). If you enter an extra monthly payment, the calculator simulates month by month: interest_i = balance * monthly_rate; payment_i = monthly_payment + extra_payment_monthly; principal_i = min(balance, payment_i - interest_i); balance_next = balance - principal_i. It sums interest and payments until the balance reaches 0 or a 1200-month safety cap is hit. If payment_i is not larger than interest_i while APR is above 0, the balance will not go down, so payoff outputs return N/A with a clear message.
Step 6: All-in total cost
The estimated all-in total cost is total_cost_all_in = vehicle_price + sales_tax_amount + fees_total + total_interest_used - rebate_cash - net_trade_credit. This gives a big-picture net cost that includes interest and accounts for rebates and trade-in (including negative equity).