Sales tax on the price minus the trade-in

Tax is the sales-tax percent times the price after trade-in is subtracted. The tax is then added to the amount financed.

The taxable amount

Trade-in is subtracted from the price first. If that result is negative, taxable amount is zero. The percent you type is applied to what remains.

That tax is cash that has to be covered. The calculator adds it to the loan: price, minus down payment, minus trade-in, plus tax. It does not assume you wrote a separate check for tax unless your down payment is large enough to cover it.

You type the percent

There is no state table. A 7% tax and an 8% tax are whatever you enter. If your state taxes the full price and ignores the trade-in, this formula will understate the tax. In that case, raise the percent or the price until the tax dollars match the bill you were given.

Title fees and doc fees are not a separate line. If they are financed, include them in the price you type so the loan matches the contract.

Tax is not interest

Sales tax does not change the rate. It changes the principal. A larger principal raises the payment and the interest over the term.

The APR field is still only the fee estimate. Do not put sales tax in the APR.

This explains how WiseCalculator treats the numbers you type. It is not a lender’s offer and it is not advice for your loan.