Methodology

Monthly payment

All three calculators use the standard formula for a fixed-rate, fully amortizing loan:

Payment = L × r ÷ (1 − (1 + r)⁻ⁿ)

Here L is the amount borrowed, r is the APR divided by 12, and n is the number of monthly payments. At 0% APR the payment is L ÷ n. The payment schedule applies each payment to that month's interest first and the rest to the balance. The last payment is adjusted by any rounding so the loan ends at exactly zero.

Amount financed

Amount financed = price − rebate − down payment − (trade-in value − amount owed on it) + tax and fees (if rolled into the loan)

If you owe more on your trade-in than it's worth, that negative equity is added to the new loan and counted in the total cost of the car.

Sales tax

Each state's rules come from its own official source and include:

• Rate: the state-level rate on a vehicle purchase, including states that use an excise tax, a title tax or a registration fee instead of sales tax.
• Trade-in credit: most states tax only the price minus your trade-in. These don't: California, Hawaii, Kentucky, Maryland, Oklahoma, Oregon, Virginia and Washington, DC. Michigan limits how much of a trade-in counts.
• Rebates: tax is charged on the price before a rebate, except in states whose rules say a rebate reduces the taxable price: Georgia, Louisiana, Minnesota, Missouri, Nebraska, New Mexico, Oregon, Utah and Virginia.
• Caps and tiers: South Carolina caps the tax at $500. Connecticut charges 7.75% instead of 6.35% when the price after trade-in is over $50,000.

When you enter a sales tax rate higher than the state's (to include county or city tax), the state's rules still apply, and the extra local rate is kept on top.

What the tax figures don't include

• Local taxes. County and city rates vary too much to apply automatically. Add yours to the sales tax field.
• Used cars and private sales. The rules are for a new car bought from a dealer. Where a state treats used cars or private sales differently, its page says so.
• Fair market value rules. Some states tax the higher of the price you paid or a book value. The calculator uses the price you enter.

How we verify the tax data

Every state's rate, trade-in rule and any special rule is checked against an official state source: the state's revenue department, DMV, statute or administrative code. Each state page links to its source and shows the date it was checked. All 50 states and DC were last checked on October 5, 2026. We also compare the rates against the Florida Department of Revenue's published table of motor vehicle tax rates in every state.

Tax rules change. Several states changed their vehicle tax or trade-in rules between 2023 and 2025, so we re-check every state at least once a year. If you spot a change before we do, please let us know with a link to the official source.

Affordability calculator

1. Monthly car budget = yearly income ÷ 12 × the share of income you choose.
2. Payment budget = car budget − insurance, gas and upkeep.
3. Car price = the highest price whose monthly payment fits the payment budget after down payment, trade-in, tax and fees. Because sales tax depends on the price, the calculator solves for the price directly instead of estimating it.

The 20/4/10 check compares your scenario with a common guideline: 20% down (counting trade-in equity), a loan of 48 months or less, and total car costs at or under 10% of gross income.

Refinance calculator

• Total saved = everything left to pay on the current loan − (everything you'd pay on the new loan + any fees paid upfront).
• Break-even is the first month where, under the new loan, what you've paid so far plus what you still owe is less than under the current loan. Fees rolled into the new loan are included because they raise its balance.

The calculator assumes a fixed rate and no prepayment penalty on the current loan. Check your loan contract for one.

Rounding and accuracy

Calculations keep full precision until the final figures, which are rounded to the cent (or to the dollar in summaries). Results are estimates. Your lender's figures may differ slightly because of how they handle the first payment date, daily interest or fees. The calculators aren't financial advice.

Maintained by Xavier E.. Questions or corrections: contact us.