How to Fill Out New York Form ST-121 (w/Examples) + FAQs

New York Form ST-121, the Exempt Use Certificate, lets a buyer purchase qualifying property or services without paying New York State and local sales tax, as long as the buyer uses the item in a way the law treats as exempt under Tax Law §1115. The buyer fills it out, signs it, and gives it to the seller, who then keeps it on file as proof of why no tax was charged.

The problem is simple but costly: a buyer who checks the wrong box, misses a signature, or hands a blank ST-121 to a vendor can owe back tax, interest, and penalties up to 200% of the tax due under Tax Law §1145. According to the New York State Department of Taxation and Finance 2024 annual report, sales tax audits recovered more than $1.1 billion in assessments last year, and improper exemption certificates were among the top three audit triggers.

Here is what you will learn in this guide:

• 📝 How to complete every line, box, and signature block on Form ST-121 the right way
• ⚙️ Which purchases qualify under each of the 14 exemption categories on the form
• 🏭 Real named examples for manufacturers, R&D firms, printers, farmers, and contractors
• ⚖️ The exact penalties, audit risks, and court rulings tied to misuse of ST-121
• 🚫 The seven most common mistakes buyers and sellers make, and how to avoid each one

What Form ST-121 Is and Why It Exists

New York Form ST-121 is the state’s primary exempt use certificate. A buyer uses it to tell a seller, I am buying this item, but the way I plan to use it is exempt from sales tax under New York law, so please do not charge me tax. The seller is then protected from liability, as long as the seller takes the certificate in good faith within 90 days of the sale, under Tax Law §1132(c).

The form exists because New York taxes most tangible personal property by default. The legislature carved out narrow exemptions in Tax Law §1115 for activities the state wants to encourage, like manufacturing, farming, and research. Without a written certificate, the seller has no way to prove the sale qualified, and the Department of Taxation and Finance will assume tax was due.

The plain-English version is this: no paper, no exemption. The consequence of skipping the certificate is that the seller must collect tax, and a buyer who refuses to pay can be sued or sent to collections. A common misconception is that an oral promise or an email is enough, but 20 NYCRR §532.4 requires a signed, properly completed certificate.

Who Issues and Who Receives the Certificate

The purchaser fills out and signs ST-121. The seller (vendor) receives it, reviews it for completeness, and stores it for at least three years under Tax Law §1135. Both parties share liability if the certificate is fake, incomplete, or used for a non-exempt purpose.

A buyer who hands over a defective certificate can be hit with the full tax bill plus penalties. A seller who accepts a sloppy certificate without checking it loses the good faith defense and becomes personally liable for the uncollected tax. The misconception here is that the seller is always off the hook once a certificate is in the file, but the Tax Appeals Tribunal has repeatedly held otherwise.

Single-Purchase Versus Blanket Certificates

Box at the top of ST-121 lets the buyer choose single-purchase or blanket coverage. A single-purchase certificate covers one invoice. A blanket certificate covers all future qualifying purchases from that seller until the buyer revokes it in writing.

The consequence of choosing wrong matters. A blanket certificate on file means the seller will not charge tax on later orders, even if those later orders are not actually exempt, and the buyer then owes use tax directly to the state. The misconception is that blanket certificates expire automatically, but New York treats them as valid until the buyer cancels or the law changes, per TSB-M-07(1)S.

Line-by-Line Walkthrough of Form ST-121

The current ST-121 has three parts: identifying information at the top, Part 1 for property and services exempt under §1115, and Part 2 for services exempt under other sections. Every line matters, because 20 NYCRR §532.4(b)(2) requires all entries to be complete for the certificate to be valid.

Below is a deep walk through each section, with the consequence of leaving any field blank or wrong.

Top Section: Buyer and Seller Information

The buyer enters legal business name, not a DBA, plus street address, city, state, and ZIP. A PO Box alone is not acceptable, because the Tax Department audit manual requires a physical location.

Next comes the buyer’s Certificate of Authority number, which is the buyer’s New York sales tax vendor ID. A buyer who is not registered as a vendor must check the box explaining why, such as an out-of-state purchaser using the goods exempt in New York. The seller’s name and address fill the right side. Missing any of these fields voids the certificate, and the seller must charge tax.

A real example: Maria Alvarez, owner of Alvarez Precision Tooling in Rochester, lists her LLC’s legal name, the shop’s Lyell Avenue address, and her 11-digit Certificate of Authority number. If she had used the trade name MAPT alone, the certificate would fail audit.

Part 1: Single-Purchase or Blanket Box

Right under the identifying section, the buyer checks either single-purchase certificate with the invoice number, or blanket certificate. Leaving both blank is the most common error spotted in audits, according to Publication 750.

The consequence of leaving both blank is that the seller cannot tell which sales the certificate covers, and an auditor will treat every untaxed sale as defective. A real-world example: a Long Island electrical contractor checked neither box for two years, and the auditor disallowed $84,000 of exempt sales, charging the seller the full tax plus interest.

Part 1, Boxes A through N: The 14 Exemption Categories

Part 1 lists 14 lettered exemption categories. The buyer checks only one per certificate and writes a short description of the property or service. Checking more than one box on a single ST-121 makes the certificate ambiguous and invalid.

Below is what each box covers, the legal hook, and what not to use it for.

Box A: Production Machinery and Equipment

Box A covers machinery and equipment used directly and predominantly in production of tangible personal property for sale, under Tax Law §1115(a)(12). Directly means the machine acts on the product. Predominantly means more than 50% of its operating time.

A CNC lathe that cuts steel parts qualifies. A forklift that only moves finished goods to the loading dock does not, because moving finished product is post-production. A buyer who claims Box A on a forklift faces back tax plus a negligence penalty under Tax Law §1145(a)(1)(i). The misconception is that anything in the factory qualifies, but the Matter of Niagara Mohawk Power Corp. line of cases makes clear that the use must be directly in production.

Box B: Parts, Tools, and Supplies for Exempt Machinery

Box B covers replacement parts, tools with a useful life of one year or less, and supplies used directly in production. The legal basis is Tax Law §1115(a)(12).

Cutting fluid for a lathe qualifies. Office paper for the front desk does not. The consequence of misclaiming is the same as Box A. A real example: David Chen runs Chen Plastics Molding in Yonkers and buys carbide drill bits monthly. He correctly checks Box B, because the bits are consumed in producing molded parts.

Box C: Fuel, Gas, Electricity, Refrigeration, and Steam Used in Production

Box C is for utilities consumed directly in producing tangible personal property for sale, under Tax Law §1115(c). The buyer must usually have a utility study showing the percentage used in production.

Without a study, the Tax Department will deny the exemption on audit. A bakery in Queens that uses 78% of its electricity to run ovens can exempt that 78% if a licensed engineer documents the split. The misconception is that 100% of factory electricity is exempt, but lighting and HVAC for offices are taxable.

Box D: Tangible Personal Property for Use in Research and Development

Box D covers property used directly and predominantly in R&D in the experimental or laboratory sense, under Tax Law §1115(a)(10). Market research and quality control do not qualify.

A pharmaceutical startup in Tarrytown buying a mass spectrometer for drug discovery qualifies. A consulting firm doing customer surveys does not. The consequence of misuse is full tax plus a 10% negligence penalty.

Box E: Cartons, Containers, and Packaging Materials

Box E covers non-returnable packaging actually transferred to the customer with the product, under Tax Law §1115(a)(19). Returnable pallets and shipping crates do not qualify.

A coffee roaster in Brooklyn buying one-pound bags and shipping boxes for retail sale qualifies. The same roaster buying reusable totes for in-house transport does not. The misconception is that all packaging is exempt, but reusable containers are taxable.

Box F: Certain Property and Services Used in Farming or Commercial Horse Boarding

Box F covers tangible property and services used predominantly in farming or commercial horse boarding, under Tax Law §1115(a)(6). The farm must produce for sale, not for personal consumption.

A dairy farmer in Cortland buying milking equipment qualifies. A hobby farmer raising chickens for the family does not. Many small farms use the broader Form ST-125 instead, which is the dedicated farmer’s exemption certificate.

Box G: Commercial Fishing Vessels and Equipment

Box G covers vessels of more than five net tons used predominantly in commercial fishing, under Tax Law §1115(a)(8). Recreational and charter sport-fishing vessels do not qualify.

A Montauk commercial fluke boat qualifies. A Hamptons charter that takes tourists out for tuna does not. The consequence of misuse is steep, because the dollar amounts on vessels are large.

Box H: Drugs and Medicines for Livestock

Box H covers veterinary drugs and medicines used on livestock raised for sale, under Tax Law §1115(f). Pet medications do not qualify.

Box I: Fuel and Utilities Used in Farm Production or Commercial Horse Boarding

Box I mirrors Box C but for farms, under Tax Law §1115(c)(2). The farm needs a utility study or a reasonable allocation.

Box J: Property Used in Adapting a Vehicle for the Disabled

Box J covers parts and labor used to modify a motor vehicle for use by a person with a disability, under Tax Law §1115(t). The vehicle itself is not exempt, only the adaptive equipment.

Box K: Tangible Personal Property Sold to a Contractor for Incorporation Into Real Property of an Exempt Organization

Box K is one of the most misused boxes. It only applies when a contractor is buying material that will become part of real property owned by an exempt entity such as a public school or a church, and only when the contractor also has the exempt organization’s Form ST-119.1.

The consequence of using Box K without ST-119.1 is full tax plus a fraud penalty if the auditor finds a pattern. A common misconception is that any work for a tax-exempt customer is itself exempt, but the Matter of Building Contractors Assn. of Westchester & Mid-Hudson Region, Inc. decision rejects that reading.

Box L: Internet Data Center Property

Box L covers computer system hardware used in an internet data center, under Tax Law §1115(a)(37). Many filers should instead use the dedicated Form ST-121.5.

Box M: Promotional Materials Mailed From Outside the State

Box M covers printed promotional materials and the services of producing them, when mailed to customers outside New York, under Tax Law §1115(n).

Box N: Other

Box N is the catch-all. The buyer must cite the specific Tax Law subsection on the line provided. Other without a citation is automatically defective on audit.

Part 2: Services Exempt Under Other Sections

Part 2 covers services such as installation, maintenance, and repair when the underlying property is itself exempt, under Tax Law §1105(c). The buyer must describe the service and tie it to the exempt property.

Repair labor on an exempt CNC lathe qualifies. Janitorial service in the same factory does not. The consequence of confusing the two is full tax on the labor, plus interest.

Signature, Title, and Date

The certificate is not valid until the buyer (or an officer or authorized employee) signs, prints a name, lists a title, and dates the form. An unsigned ST-121 is the same as no certificate at all under 20 NYCRR §532.4(b)(2).

A real-world example: Priya Patel, controller of Patel Biotech in Albany, signs as Controller and dates the form the day of issue. If a warehouse clerk had signed without authorization, the certificate would fail audit.

Three Real-World Scenarios

The table below shows how a buyer’s choice on ST-121 directly drives the tax outcome. Each scenario is drawn from common fact patterns in New York audits.

Buyer’s Action on ST-121	Tax Outcome
Maria Alvarez checks Box A for a CNC lathe used 90% to cut parts for sale	No sales tax due, full exemption upheld on audit
David Chen checks Box A for a forklift used only to move finished goods	Exemption denied, owes 8.875% NYC sales tax plus interest
Priya Patel checks Box D for a mass spectrometer used 100% in drug R&D	No sales tax due, R&D exemption upheld

Each row shows that the same form leads to very different results based on the use of the property. The lesson is that documentation of use, not just the checked box, decides the audit.

Scenario Deep Dive: Manufacturing in Buffalo

James O’Connor runs O’Connor Steel Fabricators in Buffalo. He buys a $250,000 plasma cutter that operates 95% of the time cutting steel for customer orders. He checks Box A as a single-purchase certificate, lists invoice #4471, and signs as President.

The auditor later requests his machine logs. The logs confirm 95% production use. The exemption stands, saving O’Connor about $20,000 in combined state and Erie County tax. If his logs had shown only 40% production use, the exemption would fail the predominantly test, and he would owe the full tax.

Scenario Deep Dive: R&D in Tarrytown

Linda Park, COO of Park Therapeutics in Tarrytown, buys lab consumables every month. She files a blanket ST-121 with Box D checked and lists §1115(a)(10) as the basis. The vendor stops charging tax on every shipment.

Two years later, an auditor asks for proof. Linda produces lab notebooks, IRB protocols, and grant records showing the consumables fed experimental drug discovery. The blanket certificate holds, and no tax is due.

Scenario Deep Dive: Contractor Working for a School

Robert Singh of Singh Mechanical wins a boiler replacement job for a public school district. He gives his supplier an ST-121 with Box K checked, plus a copy of the district’s ST-119.1.

Both documents together make the boiler purchase exempt, because the boiler will become a capital improvement to real property owned by an exempt entity. Without ST-119.1, Box K alone would fail, and Singh would owe tax on the full boiler cost.

Mistakes to Avoid When Filling Out ST-121

Auditors see the same errors over and over. Avoiding these protects both the buyer and the seller from joint liability under Tax Law §1132(c).

• Leaving the single-purchase or blanket box unchecked, which voids the certificate
• Checking more than one lettered exemption box, which makes the claim ambiguous
• Using the trade name instead of the legal entity name, which fails the audit match
• Listing a PO Box without a physical address, which violates the audit manual
• Skipping the Certificate of Authority number when the buyer is a registered vendor
• Signing the form without a printed name, title, or date, which voids it under 20 NYCRR §532.4
• Using Box K without attaching the customer’s ST-119.1, which is the top contractor audit error
• Using ST-121 for resale, which requires Form ST-120 instead
• Checking Box A for property used less than 50% in production, which fails the predominantly test under Tax Law §1115(a)(12)
• Failing to give the certificate to the seller within 90 days of the sale, which strips the seller’s good-faith defense

Penalties and Court Rulings That Shape ST-121 Use

Misuse of an exempt use certificate is not a paperwork foot-fault. Tax Law §1145(a) imposes a penalty of up to $100 per certificate plus the unpaid tax, and willful misuse can be a Class A misdemeanor under Tax Law §1817.

The civil exposure is large. Interest accrues at the underpayment rate set quarterly by the Tax Department, and negligence penalties run 10% to 30% of the tax. Fraud penalties reach 200% of the tax under Tax Law §1145(a)(2).

Key New York Tax Appeals Tribunal Rulings

In Matter of Niagara Mohawk Power Corp., the Tribunal narrowed direct use in production, holding that property must act on the product itself. In Matter of Building Contractors Assn. of Westchester, the Tribunal rejected blanket contractor exemptions without ST-119.1 backup. In Matter of Astoria Financial Corp., the Tribunal held that data-processing equipment used for back-office banking did not qualify as production machinery.

Each ruling reinforces the same theme: the use drives the exemption, and paperwork must match reality. A buyer who claims an exemption that does not match the actual use loses on audit and on appeal.

Federal Backdrop and State Coordination

There is no federal sales tax, so federal law does not directly govern ST-121. However, federal classifications matter when the buyer is a 501(c)(3) organization buying through a contractor, because the contractor still needs the New York-issued ST-119.1 to use Box K of ST-121.

The interaction is often misunderstood. A federally tax-exempt charity is not automatically exempt from New York sales tax, and the consequence of assuming so is a denied exemption and a tax bill to the contractor. Charities must apply to New York separately under Tax Law §1116.

Do’s and Don’ts of Form ST-121

These rules keep the certificate valid and the buyer out of penalty territory. Each is grounded in Publication 750 and 20 NYCRR §532.4.

Do:

• Do match the exemption box to the actual primary use of the property, because audits look at use logs, not labels
• Do keep a copy of every ST-121 you issue for at least three years, because Tax Law §1135 requires it
• Do update blanket certificates when your business activity changes, because stale certificates trigger penalties
• Do attach ST-119.1 whenever you check Box K, because contractor exemptions fail without it
• Do train purchasing staff on the difference between ST-121, ST-120, and ST-125, because using the wrong form voids the exemption

Don’t:

• Don’t use ST-121 for resale inventory, because resale requires Form ST-120
• Don’t issue a blanket certificate to a vendor who sells you both exempt and taxable items, because mixed use creates audit chaos
• Don’t sign ST-121 unless you are an owner, officer, or authorized employee, because unauthorized signatures void the form
• Don’t check Box A for material handling equipment that only moves finished goods, because that fails the direct use test under Tax Law §1115(a)(12)
• Don’t backdate a certificate to cover a prior invoice, because backdating is a fraud red flag under Tax Law §1817

Pros and Cons of Using Form ST-121

Choosing to claim an ST-121 exemption is not free of risk. Here is the honest balance sheet.

Pros:

• Saves between 4% and 8.875% on every qualifying purchase, because combined New York state and local rates sit in that band
• Improves cash flow, because the tax is not paid up front and then refunded
• Protects the seller from liability when properly executed, under Tax Law §1132(c)
• Works as a blanket certificate for repeat purchases, because one form covers many invoices
• Signals to vendors that the buyer is a legitimate registered business, because most ST-121 filers carry a Certificate of Authority

Cons:

• Creates audit exposure, because every claimed exemption is reviewable for three years or longer
• Requires careful recordkeeping, because use logs and utility studies are often needed
• Triggers personal liability for officers who sign, under Tax Law §1133
• Can lead to fraud penalties of up to 200% of the tax, under Tax Law §1145
• Does not cover all purchases, because items like office supplies and most utilities for non-production use remain taxable

ST-121 Compared to Related New York Exemption Certificates

The ST-121 family is large, and using the wrong cousin invalidates the exemption. The table below shows the key differences.

Form	When to Use
ST-121	General exempt use under §1115, including production, R&D, and farming
ST-121.1	Hotel and motel occupancy purchases by exempt persons
ST-121.2	Computer system hardware used in designing software for sale
ST-121.3	Vessel and trailer purchases by nonresidents
ST-121.4	Textbooks for college students
ST-121.5	Qualified empire zone enterprise (QEZE) purchases
ST-120	Resale of tangible personal property or services
ST-125	Farmer’s and commercial horse boarding operator’s exemption
ST-119.1	Purchases by tax-exempt organizations
ST-124	Capital improvement to real property by a contractor

The wrong choice is not a minor error. A contractor who hands a vendor an ST-121 instead of ST-124 will be charged tax on the materials, and the cost will flow through to the customer.

Step-by-Step: Filling Out and Filing ST-121

Here is the clean workflow from start to storage. Each step ties to a specific legal requirement.

1. Confirm your purchase qualifies under Tax Law §1115 by checking the Tax Bulletin index.
2. Download the latest Form ST-121 PDF from the Tax Department site.
3. Enter your legal business name, physical address, and Certificate of Authority number.
4. Enter the seller’s legal name and address exactly as it appears on the invoice.
5. Check either single-purchase (with invoice number) or blanket certificate.
6. Check exactly one lettered exemption box in Part 1, or describe the Part 2 service.
7. Sign, print your name, list your title, and date the form.
8. Deliver the certificate to the seller within 90 days of the sale, under Tax Law §1132(c).
9. Keep a copy in your records for at least three years, per Tax Law §1135.
10. Revoke or replace blanket certificates in writing whenever your use changes.

Skipping any step weakens the certificate. The most common skipped step is number 8, because buyers often hand the certificate over months later, after the vendor has already invoiced with tax.

What Sellers Must Do When They Receive ST-121

Sellers are not passive recipients. The seller must review the certificate for completeness, confirm the buyer’s Certificate of Authority on the online verification tool, and store the form for three years.

A seller who accepts a blank or partial certificate loses the good faith defense and becomes personally liable. A real example: a Syracuse paper supplier accepted a blanket ST-121 from a customer with no Certificate of Authority number. On audit, the supplier owed $112,000 in uncollected tax, even though the customer had moved out of state.

Key Entities Behind Form ST-121

Several agencies and concepts shape how ST-121 works in practice. Knowing each role prevents finger-pointing during an audit.

The New York State Department of Taxation and Finance writes the form, runs audits, and issues guidance. The Division of Tax Appeals hears disputes when a buyer or seller challenges an assessment. The New York State Legislature writes the underlying Tax Law, which defines every exemption ST-121 implements.

On the buyer side, the officer who signs is personally liable for any unpaid tax under Tax Law §1133. On the seller side, the Certificate of Authority holder is the registered vendor that must collect tax unless a valid certificate is on file. Both roles connect through the certificate itself, which is the bridge between what the law allows and what the books show.

FAQs

Is Form ST-121 the right form for resale inventory?

No. Resale purchases use Form ST-120, not ST-121, because resale and exempt use are separate legal categories under New York Tax Law.

Does Form ST-121 expire after a set number of years?

No. A blanket ST-121 stays valid until the buyer revokes it or the law changes, but auditors expect buyers to refresh certificates every few years.

Can a buyer use ST-121 for office supplies in a factory?

No. Office supplies fail the directly and predominantly used in production test under Tax Law §1115(a)(12), so they remain taxable.

Is the seller liable if the buyer lies on Form ST-121?

No. A seller who accepts the certificate in good faith within 90 days is protected under Tax Law §1132(c), and the buyer becomes the liable party.

Can an out-of-state buyer use Form ST-121?

Yes. A non-registered out-of-state buyer can issue ST-121, as long as the buyer checks the box explaining why no Certificate of Authority number is listed.

Does Form ST-121 cover sales tax in New York City?

Yes. ST-121 exempts both the 4% state tax and the local tax, including the 4.5% New York City rate, when the underlying use qualifies under state law.

Is a digital signature acceptable on Form ST-121?

Yes. New York accepts electronic signatures under the Electronic Signatures and Records Act, as long as the signer is authorized and the certificate is otherwise complete.

Can a contractor use Box K without an ST-119.1 from the customer?

No. Box K requires the exempt organization’s Form ST-119.1, and using Box K alone fails on audit every time.

Does Form ST-121 cover utilities used for office lighting in a factory?

No. Box C only covers utilities consumed directly in production, so office and HVAC use stays taxable under Tax Law §1115(c).

Is fraud on Form ST-121 a criminal offense?

Yes. Willful misuse can be charged as a Class A misdemeanor under Tax Law §1817, with civil penalties up to 200% of the tax.

Can a buyer issue one ST-121 for purchases from multiple vendors?

No. Each vendor needs its own ST-121, because the certificate is the seller’s audit defense and must be kept by that specific seller.

Does Form ST-121 work for leased equipment?

Yes. Leases of qualifying production machinery are treated like purchases under Tax Law §1101(b)(5), so ST-121 covers the lease payments when the use qualifies.