The tax credit: the trade-in's hidden bonus
A dealer trade-in is worth its negotiated value PLUS the tax it shields (in credit states). That changes the private-sale comparison: selling privately typically fetches more gross, but the trade's tax shield claws back $480-plus on mid-size deals. Rule of thumb in credit states: private sale needs to beat the trade offer by more than the tax shield to be worth the hassle — in no-credit states, private selling wins more often.
Payoffs and negative equity in the same math
Still owe on the trade? The dealer pays your lender and the difference flows through the deal: positive equity reduces what you finance; negative equity gets added to the new loan (and note — the tax credit is based on the trade's value, not your equity). The calculator's "still owed on trade" field wires this correctly and flags negative equity — the trap covered in upside down on a car loan.
Negotiate the three numbers separately
- The car's price — settle it before mentioning a trade.
- The trade-in value — armed with 2–3 online instant offers as your floor.
- The financing — against a pre-approval you brought.
Dealers blend these into "what monthly payment works for you?" precisely because a blended number hides which lever they moved. Three separate numbers, then let the calculator assemble the deal — including whether rolling tax and fees into the loan is worth it.
State quirks worth knowing
- No-sales-tax states (AK, DE, MT, NH, OR) make the credit question moot — but registration-based fees can apply.
- Special systems: Georgia's one-time TAVT and North Carolina's highway-use tax behave like sales tax with their own rates; South Carolina caps the fee at $500 outright.
- Local add-ons: county/city taxes stack 1–5% on the state rate in much of the country — our calculator's rate field stays editable for your real combined rate.