Calculate monthly car payments, total cost of financing, and compare loan terms with trade-in and down payment adjustments.
This tool runs a vehicle price, trade-in value, down payment, APR, and loan term through the standard installment-loan formula to produce a monthly payment, total of payments, and total interest. Trade-in and down payment are subtracted from the price before the payment is calculated, so increasing either reduces the amount financed directly. The most common surprise: whether sales tax is charged on the full price or on the price minus trade-in credit depends on the state, and the tool only applies what you enter, so an omitted or misapplied tax figure will understate the real amount financed.
A concrete input and expected output from the current implementation.
Input
Vehicle price $34,000, trade-in credit $4,000, down payment $0, amount financed $30,000, APR 6%, term 60 months
Expected output
Monthly payment: $579.98. Total of payments: $34,799.04. Total interest: $4,799.04.
Monthly rate is 6%/12 = 0.5%; applying the standard amortization formula M = P*r / (1 - (1+r)^-n) to a $30,000 principal over 60 months at 0.5% gives an unrounded payment of $579.984, displayed rounded to $579.98. The total of payments and total interest are derived from that unrounded payment (579.984 x 60), giving $34,799.04 total paid and $4,799.04 in interest, rather than from multiplying the rounded, displayed $579.98 figure by 60.
The monthly payment is computed as M = P * r / (1 - (1+r)^-n), where P is the amount financed, r is the APR divided by 12, and n is the loan term in months. This assumes a fixed rate and equal monthly payments with interest accruing on the declining balance, matching how most retail auto loans are structured.
Trade-in value and down payment are subtracted from the vehicle price to arrive at the amount financed before the payment formula runs. Any sales tax, title, or documentation fees you choose to enter are added back into the financed amount rather than paid separately, so including or omitting them changes the principal the calculator amortizes.
No. It only applies figures you enter. If your state taxes the price after trade-in credit, add that adjusted tax amount to the financed total yourself; if you leave tax and fees out, the result reflects financing on price minus trade-in and down payment only, not your total out-the-door cost.
You can, by entering a negative trade-in value or adding the shortfall to the vehicle price, which increases the amount financed. The calculator does not detect negative equity automatically, so you have to compute the payoff-versus-value gap yourself before entering it.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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