How to Fill Out NY Form ST-121.1: Tractor and Trailer Exemption Certificate

New York Form ST-121.1 is the sales tax exemption certificate you give a seller to buy a qualifying tractor, trailer, semitrailer, or omnibus — along with parts, equipment, and repair services for those vehicles — without paying state or local sales tax. The certificate is issued by the New York State Department of Taxation and Finance and is available as a fillable PDF on the agency’s website. You complete it, hand it to the seller at the time of purchase, and keep a copy for your records. The form never goes to the state.

Before you fill anything out, make sure your vehicle actually qualifies. The thresholds are strict, and using the form on the wrong purchase carries real penalties.

Which Vehicles Qualify

Two categories of vehicles are covered, each with its own test under New York Tax Law.¹

Tractors, trailers, and semitrailers. The vehicle must be used in combination, and the gross vehicle weight of that combination must exceed 26,000 pounds. A trailer or semitrailer still qualifies when the towing vehicle is a truck rather than a tractor, as long as the combined weight clears the threshold.

Omnibuses. The bus must weigh at least 26,000 pounds, measure at least 40 feet long, and carry passengers for hire under a certificate or permit from the New York State Department of Transportation or an appropriate federal agency.

Combinations at or below 26,000 pounds do not qualify. Omnibuses that fall short on size, weight, or for-hire operation do not qualify. A standard delivery van, pickup truck, or city taxi is outside the scope of this form no matter how it’s used.

What You Can and Cannot Buy Tax-Free

For qualifying tractors, trailers, and semitrailers, the exemption extends to parts and property installed on the vehicle for equipping, maintaining, or repairing it, plus the installation, maintenance, and repair services performed on those vehicles or their installed components.² For qualifying omnibuses, it covers parts, equipment, lubricants used in operation, and the same range of repair and maintenance services.

Several things the form does not cover:

Motor fuel and diesel motor fuel, which are taxed separately.
Hand tools, road flares, road reflectors, and similar uninstalled items, unless sold as part of the vehicle’s original equipment.
Shop equipment such as service jacks, tire changers, parts washers, battery chargers, and truck or tractor washers.
Repair work on a vehicle that doesn’t meet the weight or use test, even if you own other vehicles that do qualify.

How to Fill Out the Form

Download the fillable PDF from tax.ny.gov. The form runs one page, with definitions and instructions on the back.

Seller and Purchaser Information

Enter the seller’s name at the top and your name and address exactly as they appear on your business records. Then check one of two boxes: blanket certificate (covers ongoing purchases of the same general type from this seller) or single-purchase certificate (one transaction only).

Identification Numbers

Enter every ID number that applies to you:

Sales tax vendor identification number, if you’re a registered sales tax vendor.
U.S. Department of Transportation number, for movers of household goods.
Highway use tax identification number, for highway use tax filers.
NYS DOT case number, for omnibus owners — this is the number on your certificate or permit from the New York State Department of Transportation.

Registered vendors have a meaningful advantage. If you hold a valid sales tax vendor ID, you can use ST-121.1 to buy parts and equipment tax-free even when you don’t yet know whether the property will go on a qualifying vehicle. If it later ends up on a nonqualifying one, you self-assess and remit the tax at that point. Purchasers without a vendor registration can only claim the exemption when they know, at the time of purchase, that the item is going on a qualifying vehicle.²

Exemption Reason Checkboxes

Six checkboxes sit in the middle of the form, three for tractors, trailers, and semitrailers and three for omnibuses. Mark every box that applies to the purchase:

A qualifying tractor, trailer, or semitrailer.
Parts or property for installation on qualifying tractors, trailers, or semitrailers.
Installation, maintenance, or repair services on those vehicles or their installed components.
A qualifying omnibus.
Parts, equipment, and lubricants for a qualifying omnibus.
Installation, maintenance, or repair services on a qualifying omnibus or its parts and equipment.

Signature and Certification

Print your name and title (owner, partner, corporate officer), sign, and date. The certification language on the form warns that willfully issuing a false exemption certificate to evade tax can be charged as a felony under New York law.

Blanket Certificates vs. Single-Purchase Certificates

If you buy parts or services from the same vendor regularly, a blanket certificate cuts down on paperwork. Once on file, it covers the first purchase and all future purchases of the same general type of property or service from that seller. Each later sales slip or invoice must show your name, address, and the identification number listed on the original certificate.

The form sets no expiration date for blanket certificates. The seller, however, must keep the certificate on file for at least three years from the due date of the sales tax return on which the last covered sale was reported.³ Vendors often ask for a refreshed certificate periodically to keep their records current.

What the Seller Must Do

The seller has to collect a properly completed certificate within 90 days of delivering the property or service. If that window closes without a complete certificate, the sale is treated as taxable and the vendor owes the uncollected tax.⁴ Once the certificate is on file, the burden of proving the purchase was actually exempt shifts to you as the purchaser. The seller is protected if the certificate was accepted in good faith, meaning the seller had no reason to believe it was false or that the purchase didn’t qualify.³

Good faith is not a rubber stamp. A seller who knows the buyer is buying parts for a light-duty pickup that clearly falls below the 26,000-pound threshold does not get liability protection by accepting the certificate anyway. The standard is ordinary care.

Penalties for Misuse

Using ST-121.1 on purchases that don’t actually qualify is expensive, and the penalties climb depending on whether the misuse was careless or deliberate.

Failure to pay tax that was due: 10 percent of the tax owed for the first month, plus 1 percent for each additional month, up to a 30 percent maximum. Interest runs on the unpaid amount at 14.5 percent per year or the underpayment rate set by the Tax Commissioner, whichever is higher.⁵
Issuing a false or fraudulent exemption certificate: 100 percent of the tax that should have been paid, plus $50 for each fraudulent certificate issued.⁶
Criminal charges: willfully issuing a false exemption certificate can be prosecuted as a felony, carrying potential fines and jail time.

If you buy something tax-free with this form and later use it on a nonqualifying vehicle, you owe the tax at that point. Registered vendors who claimed the exemption speculatively are expected to self-assess and remit when the property ends up in a taxable application.

When You Need a Different Form

Using the wrong exemption certificate is a common mistake. ST-121.1 applies only to the qualifying tractors, trailers, semitrailers, and omnibuses described above. Two related forms cover different territory:

Form ST-121, the Exempt Use Certificate, is the general-purpose certificate for production, manufacturing, research and development, and other exempt uses listed in Tax Law Section 1115. Manufacturing machinery or lab equipment goes on ST-121, not ST-121.1.⁷
Form ST-125, the Farmer’s and Commercial Horse Boarding Operator’s Exemption Certificate, covers farm machinery, equipment, and supplies used predominantly in agricultural production or commercial horse boarding. A farm tractor used for field work belongs on ST-125.⁸

The dividing line is weight and commercial highway use. ST-121.1 exists for heavy vehicles hauling freight or running passenger routes. If your purchase doesn’t involve a 26,000-pound-plus combination or a qualifying omnibus, you need a different form.

1
New York State Senate. New York Tax Law 1115 – Exemptions From Sales and Use Taxes
2
New York State Department of Taxation and Finance. ST-121.1 – Exemption Certificate for Tractors, Trailers, Semitrailers, or Omnibuses
3
New York State Department of Taxation and Finance. Exemption Certificates for Sales Tax
4
New York State Senate. New York Tax Law 1132 – Powers and Duties of the Tax Commission
5
New York State Senate. New York Tax Law 1145 – Penalties and Interest
6
New York State Department of Taxation and Finance. Sales and Use Tax Penalties
7
New York State Department of Taxation and Finance. New York State and Local Sales and Use Tax Exempt Use Certificate
8
New York State Department of Taxation and Finance. Exemptions for Farmers and Commercial Horse Boarding Operators