Overview
This calculator covers the three situations that come up at the county assessor's counter: a dealer purchase with a trade-in, a private-party sale taxed on the full price, and a qualifying gift or family transfer that owes no sales tax at all under Idaho's ST-133 exemption.
01 - Official fees
Idaho car sales tax fees at a glance
| Fee | Amount | Notes |
|---|---|---|
| Standard rate | 6% | statewide, no county or city add-on |
| Dealer sale base | price − trade-in | |
| Private sale base | full purchase price (bill of sale) | |
| No bill of sale | NADA average trade-in value used instead | |
| Qualifying gift or family sale | $0 tax | Form ST-133 / ST-133GT |
| Late title filing (30+ days) | $20 flat penalty |
Figures verified June 2026 against official sources (listed below). Always confirm the final amount with your county DMV/assessor's office (Idaho Transportation Department) - counties can add small local fees.
03 - Same state, other costs
More Idaho vehicle costs
04 - Common questions
Idaho car sales tax FAQ
Is Idaho vehicle sales tax really just 6% everywhere?
Yes - Idaho is one of the more straightforward states here. Even resort cities like McCall and Ketchum that add a local option tax on lodging and retail generally carve out motor vehicles, so 6% is the number almost every buyer pays.
Does Idaho tax the sale price or a presumptive book value?
The actual price on your bill of sale, full stop - no mandatory comparison against a value chart like Texas's SPV. The catch: if you don't have a bill of sale, the county defaults to the NADA average trade-in value, and if your reported number looks suspiciously low for the vehicle, they can assess tax on fair market value instead.
I'm buying private-party - can I still deduct a trade-in?
No. Idaho's trade-in credit only applies when a licensed dealer takes your old vehicle into inventory as part of the deal. A private seller taking your old car in a swap doesn't reduce your taxable price at all - you owe 6% on the full agreed price.
Do I owe tax if my parent or sibling gives me their car?
No, if it's a genuine gift or a sale between parents, children, grandparents, grandchildren, or siblings (Idaho calls this the 'second degree of consanguinity'). Both parties sign Form ST-133 or ST-133GT and file it with the title. Aunts, uncles, cousins, and in-laws don't qualify - that transfer is taxed like any other sale.
What if the original owner never paid Idaho sales tax on the vehicle?
The family/gift exemption only works if sales or use tax was already paid on the vehicle at some point in its history. If it wasn't - say it was previously registered somewhere with a tax exemption of its own - the exemption chain breaks and the new owner may owe tax despite the family relationship.
When and where do I actually pay the tax?
At your county assessor's motor vehicle desk, when you title the vehicle - typically within 30 days of the purchase. There's no separate 'tax office' the way some states split it; one county visit handles tax, title, and registration together.
05 - Receipts
Official sources
Every number on this page comes from these documents - check them yourself.