If you're buying or selling a car in Idaho, you've probably heard the term "bill of sale" tossed around. It sounds simple, but getting it wrong can slow down your title transfer, create tax headaches, or even leave you on the hook for a car you don't own anymore.

Idaho is one of the fastest-growing states in the country. The state's population passed 2 million people in 2024 and grew by another 1.4% to reach roughly 2,029,733 residents in 2025, according to Idaho Department of Labor estimates drawn from U.S. Census Bureau data (idahoatwork.com). More people moving in means more cars changing hands every year, and that makes it worth knowing exactly what Idaho expects from a bill of sale.

This guide walks through when you need one, what it must include, how it fits into the title transfer process, and where to get a copy — all sourced from the Idaho Transportation Department (ITD) and other official state agencies.

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What Is an Idaho Bill of Sale?

An Idaho bill of sale is a signed document that records the transfer of a vehicle from a seller to a buyer. In Idaho, the official version is Form ITD 3738, issued by the Idaho Transportation Department (itd.idaho.gov).

It typically includes:

• Full names and addresses of both buyer and seller

• Vehicle description (year, make, model, VIN)

• Odometer reading

• Sale price and date of sale

• Signatures of both parties

Think of it as a receipt with legal weight. It doesn't replace the title, but it backs up the sale price and ownership change if anyone — the DMV, an insurance company, or a court — ever needs proof of what happened.

Do You Actually Need One in Idaho?

Here's where Idaho differs slightly from some other states. Most Idaho titles (the standard blue title) have a built-in space where the seller can write down the sale price. If that space is filled out and signed, you technically don't need a separate bill of sale (dmv.org).

You do need a standalone Form ITD 3738 if:

• The title doesn't have room to declare a sale price

• The title is missing, damaged, or unclear

• You're using a Bill of Sale in place of a title under Idaho's Conditional Title Statement of Facts process, which the ITD notes involves extra steps (itd.idaho.gov)

• The buyer's lender, insurer, or county assessor's office asks for one specifically

Even when it's not strictly required, the ITD recommends completing one anyway for every private sale, since it gives both sides a clear paper trail if a dispute comes up later.

What Information Goes on Form ITD 3738

The Idaho Transportation Department's official form asks for specific fields, and missing any of them is one of the most common reasons a bill of sale gets rejected at the county assessor's office. Based on the current ITD form (itd.idaho.gov), you'll need:

Vehicle Details

• Vehicle Identification Number (VIN)

• Title number

• Year, make, and model

• Weight, length, and width (for trailers, mobile homes, or motor homes)

• Any brands on the title, such as "Rebuilt Salvage" or "Reconstructed"

• Odometer reading, including whether the mileage is actual, exceeds mechanical limits, or exempt

Seller Information

• Full legal printed name

• Physical address

• Idaho driver's license number or SSN/EIN if a business

• Signature

Buyer Information

• Full legal printed name

• Physical address (and mailing address, if different)

• Signature

Sale Details

• Sale price

• Date of sale

Double-check the VIN against the title and the vehicle itself before signing. A single mismatched digit can hold up the entire title transfer at the county office.

Idaho Bill of Sale Requirements at a Glance

If there's a lien on the vehicle, the lienholder has to release their interest first — either through a paid-off loan or Idaho's Satisfaction of Lien form (ITD 3726) — before the title can be transferred.

Sales Tax on Idaho Vehicle Sales

Idaho charges a flat 6% sales tax on the purchase price of a vehicle, whether it's bought from a dealership or a private seller. This is a state excise tax under Idaho Code § 63-3619, confirmed by the Idaho State Tax Commission (tax.idaho.gov).

A few things worth knowing:

• The tax is based on the sale price written on the title or bill of sale, not a separate estimate.

• If the county assessor suspects the listed price is artificially low, they can assess tax based on the vehicle's fair market value instead.

• Sales between certain immediate family members (parent-child, grandparent-grandchild, siblings) can be tax-exempt if the family member already paid sales tax when they originally bought the vehicle.

• Idaho does not add local city or county sales tax on top of the state rate for vehicles, which keeps the math simpler than in many other states.

This is exactly why the sale price on your bill of sale needs to match what's on the title. Entering a false selling price on either document is a felony under Idaho Code § 49-518(5).

Odometer Disclosure: A Federal Requirement, Not Just a State One

Odometer fraud is a federal crime, and the disclosure requirement comes from the National Highway Traffic Safety Administration (NHTSA), not just Idaho state law.

Under 49 CFR Part 580, a written odometer disclosure is required for most vehicles that are:

• Under 16,000 lbs. gross vehicle weight rating, and

• Less than 20 model years old at the time of transfer (ecfr.gov)

Vehicles over 16,000 lbs. GVWR, non-self-propelled vehicles (like some trailers), and sufficiently old vehicles are exempt. On the Idaho bill of sale form, this shows up as the odometer reading field, where you'll mark whether the mileage is actual, "not actual," exceeds mechanical limits, or exempt.

Common Mistakes to Avoid

A few small errors cause most of the delays people run into at the county assessor's office:

• Leaving the odometer box blank. Every transfer needs a mileage entry, even if it's marked "exempt."

• Mismatched sale prices. If the title and bill of sale show different amounts, expect questions — and possibly a tax reassessment.

• Skipping the lien release. If a lender's name is still on the title, the sale can't be finalized until that's cleared.

• Missing the 30-day window. Waiting too long to title the vehicle after purchase can trigger a late penalty.

• Illegible or incomplete VIN. Copy it directly from the title or the vehicle's dashboard plate, not from memory.

Private Sale vs. Dealer Sale: Does the Bill of Sale Differ?

Not every car changes hands the same way, and the paperwork shifts a little depending on who's selling.

Private party sales rely on the buyer and seller filling out the title's sale price section or completing Form ITD 3738 themselves. There's no dealer paperwork involved, so it's on both people to make sure every field is accurate and legible.

Dealer sales typically come with their own bill of sale generated by the dealership's system, along with a separate purchase agreement. Dealers usually handle the title application and tax collection directly, which is one reason buying from a dealer can feel more streamlined — though it often costs more than buying private.

Family transfers sit somewhere in between. A bill of sale is still useful for the record, but the sale may qualify for a sales tax exemption if it's between a parent and child, grandparent and grandchild, or siblings, and the vehicle already had Idaho sales or use tax paid on it once.

Whichever category applies, the core requirement stays the same: the ITD needs an accurate record of who sold the vehicle, who bought it, and for how much.

Why the Bill of Sale Protects Both Sides

It's easy to think of a bill of sale as paperwork for the DMV's benefit, but it protects buyers and sellers just as much.

For the seller, it's proof the vehicle changed hands on a specific date. If a parking ticket, toll violation, or accident happens after the sale but before the buyer registers the car, a signed bill of sale with a date can help show the seller no longer owned the vehicle at that point.

For the buyer, it's a record of exactly what was agreed to — the price, the vehicle's identity, and the seller's confirmation that they had the right to sell it. If a dispute comes up later about what was included in the sale or what price was actually paid, this document is the first thing most people reach for.

Given that private-party sales don't come with a dealership's legal team or standard contracts, this simple form is often the only written protection either side has.

Where to Get the Idaho Bill of Sale Form

The official Form ITD 3738 is available as a free PDF directly from the Idaho Transportation Department's website (itd.idaho.gov). County assessor's motor vehicle offices also keep copies on hand if you'd rather pick one up in person.