In most states, contractors pay sales tax on the materials they buy for a job and charge no sales tax on labor, so the question of whether contractors pay sales tax on materials and labor usually comes down to materials. But the amount owed, who writes the check, and whether labor gets taxed at all depend on how your contract is written, what kind of work you’re doing, and which state you’re working in. Five states have no general sales tax at all: Alaska, Delaware, Montana, New Hampshire, and Oregon. Everywhere else, the first thing to settle is whether you’re the end user of the materials or a reseller passing them through to your client.
Who Pays Tax on the Materials
Every state’s rules revolve around a single question: when you buy lumber, pipe, or wiring for a project, are you the end user, or are you reselling the material to your client? The answer decides where the tax gets collected and on what dollar amount.
If you’re the consumer, you pay sales tax to the material supplier at the time of purchase. The tax applies to whatever you paid the supplier. Your invoice to the client doesn’t carry a separate sales tax line because the tax is already baked into your costs. You can roll that cost into your price, but you can’t break it out on the client’s bill as if you were collecting tax on the state’s behalf.
If you’re the retailer, you buy materials tax-free from the supplier using a resale certificate and then charge your client sales tax on the materials portion of the final bill. Because retailers typically mark materials up, the tax the client pays is calculated on the higher price. A contractor who buys $1,000 of lumber and marks it up to $1,200 collects tax on $1,200. In a state with a 6% rate, the client pays $72 instead of the $60 the contractor would have paid as a consumer.
Getting the role wrong in either direction creates trouble. Pay tax as a consumer when the state treats you as a retailer, and you’ve overpaid. Collect tax as a retailer when the state treats you as a consumer, and you’ve charged a tax you had no authority to collect, which some states treat as a serious violation.
How Your Contract Changes the Answer
The single biggest factor in determining whether you’re a consumer or a retailer is how your contract is structured. Two contractors on the same street, using the same materials, can have opposite tax obligations based purely on how their agreements read.
Lump-Sum Contracts
In a lump-sum or fixed-price contract, you agree to complete the work for one price that bundles materials, labor, overhead, and profit. Because the materials aren’t separately stated, most states treat you as the final consumer. You pay sales tax to your suppliers when you buy the materials, and you don’t charge your client any additional sales tax. The tax is part of your cost of doing business.
The practical consequence is simple: price your bid to cover the sales tax you’ll pay on materials. Contractors who forget end up absorbing it out of margin. And if you fail to pay tax to your suppliers under a lump-sum contract, the state will come looking for it during an audit.
Time-and-Materials Contracts
A time-and-materials contract bills the client separately for labor and for materials. This separation can shift your role to retailer in states that recognize the distinction. As a retailer, you purchase materials tax-free using a resale certificate and collect sales tax from the client on only the materials portion of the invoice.
The catch is that many states impose strict requirements for what counts as a genuinely separated contract. Simply listing materials on the invoice isn’t always enough. The contract itself often needs to establish that the client is purchasing materials from you, not just receiving an itemized breakdown of your costs. If the language is ambiguous, the state can reclassify the contract as non-separated and treat you as the consumer.
Non-Separated Contracts
Non-separated contracts are hybrids. They provide some billing detail but don’t meet the state’s specific requirements for a true time-and-materials arrangement. Most states treat these the same as lump-sum contracts: you’re the consumer and you owe tax on your material purchases. The default in nearly every state favors consumer treatment when the contract doesn’t clearly qualify for retailer status, so ambiguity works against you.
Capital Improvements vs. Repairs
Even when a contract is clearly structured, the type of work can override the contract-based rule. Most states automatically classify a contractor performing a permanent real property improvement as the consumer of the materials, regardless of what the contract says.
A real property improvement means permanently attaching materials to a building or land so they become part of the real estate. Pouring a foundation, running electrical wiring through walls, installing built-in cabinetry, or plumbing a bathroom all qualify. Once those materials are incorporated, they stop being standalone products and become part of the structure. The contractor pays tax on the materials at purchase, and the client’s bill doesn’t carry a separate sales tax charge.
Repairs and maintenance of tangible personal property often follow different rules. Replacing a compressor in a commercial HVAC unit, for instance, might make you the retailer of that compressor in states that distinguish between improvements and repairs. The logic is that a repair part retains its identity as personal property rather than becoming part of the real estate.
The dividing line is fact-specific. The most common test looks at permanence: would removing the installed item cause substantial damage to the building? If yes, it’s almost certainly an improvement. A built-in dishwasher that’s permanently wired is an improvement; a freestanding refrigerator that plugs into an outlet is tangible personal property. States publish guidance on specific items, and checking that guidance before starting a project is worth the time.
Is Construction Labor Taxed?
Most states do not impose sales tax on construction labor. When a contractor bills separately for labor and materials, the labor portion is typically exempt. This is one reason time-and-materials contracts can be attractive to a client: they pay sales tax only on the materials, not on the total project cost.
A handful of states take a broader approach and tax services, including construction labor. Arizona and New Mexico are the most prominent examples, though their specific rules and rates differ. If you work in a state that taxes services, your labor charges may be subject to a transaction privilege tax or gross receipts tax rather than a traditional sales tax, but the practical effect is the same: the total bill to the client is higher.
Under a lump-sum contract where you’re the consumer, the labor question is largely moot. You’ve already paid tax on the materials, and the single-price invoice to the client isn’t itself taxable. The labor distinction only matters when materials and labor are billed separately.
Tools, Equipment, and Consumables
Here’s a rule that catches newer contractors off guard. Your tools, equipment, and consumable supplies are always taxable to you, no matter what kind of contract you’re working under. A resale certificate covers materials you’re reselling to your client or incorporating into the project. It does not cover the drill you used to install those materials, the saw blades you burned through cutting them, or the fuel in your generator.
Scaffolding, safety equipment, sandpaper, welding gas, thread-cutting oil: all consumed by your business, not by the client’s project. You owe sales or use tax on every one of those purchases. The same goes for rentals of heavy equipment like excavators and boom lifts. In most states, renting tangible personal property is a taxable transaction, with tax calculated on the rental payments.
Auditors routinely check whether contractors have been using resale certificates to buy supplies and tools tax-free. If you’ve been running job-site consumables through your resale certificate, expect an assessment for the unpaid tax plus penalties.
Resale Certificates and Their Limits
When you qualify as a retailer, a resale certificate is the document that lets you buy materials tax-free from suppliers. You present it to the supplier, who keeps it on file as proof they weren’t required to collect tax. The supplier’s protection depends on having a valid certificate, so expect them to ask.
To obtain a resale certificate, you first need a valid seller’s permit from the state where you’re collecting tax. The certificate itself typically requires your permit number, business name and address, a description of the items, and a signed statement that the materials are for resale. Suppliers may ask for updated certificates periodically.
Not every state allows contractors to use resale certificates. The Multistate Tax Commission’s uniform resale certificate, which many states accept, explicitly notes exceptions. Kansas prohibits contractors from using it to purchase materials tax-free. Nevada states that contractors are generally consumers of tangible personal property and should not use the certificate. Vermont bars contractor use entirely.1Multistate Tax Commission. Uniform Sales and Use Tax Resale Certificate — Multijurisdiction Using a resale certificate in a state that doesn’t permit it for contractors is a fast path to audit trouble.
A common compliance trap arises when you buy materials tax-free with a resale certificate but then use them yourself instead of reselling to a client. Leftover materials from a project get used to fix up your own office; a project’s contract type changes after purchasing has started. When materials bought for resale end up consumed by you, you owe use tax on the original purchase price. Self-assessing and remitting that tax is your responsibility, and most states provide a line on the regular sales tax return for exactly this purpose.
Hold on to your resale certificates, purchase invoices, and sales tax returns. State audit windows generally run three to four years from the filing date, but many tax professionals recommend keeping exemption certificates permanently, since the burden of proving an exempt sale falls on the seller who accepted the certificate.
Use Tax on Out-of-State Purchases
When you buy materials from an out-of-state supplier or online vendor who doesn’t collect your state’s sales tax, you owe use tax directly to your state. Federal tax law defines use tax as a “compensating” tax that mirrors the general sales tax, meaning it’s imposed at the same rate on items that escaped sales tax at the point of purchase.2Legal Information Institute. 26 USC 164(b)(5) – Compensating Use Tax If your state sales tax rate is 6.5%, your use tax rate is 6.5%.
This comes up whenever you source specialized materials from manufacturers in states with lower or no sales tax. The savings from buying out of state disappear if you’re properly self-assessing use tax, which is the point of the tax. States designed it to prevent cross-border shopping from eroding their revenue base.
Track every out-of-state purchase and report use tax on your regular state filings. Auditors cross-reference expense records against reported use tax, and gaps between the two are among the easiest audit findings to make. Most states impose penalties for unpaid use tax that scale with how late the payment is, and interest accrues from the original due date.
Government and Nonprofit Projects
Working for a government agency or tax-exempt nonprofit can change your sales tax obligations, but not automatically. In many states, contractors can purchase materials for these projects tax-free by presenting a special exemption certificate tied to the client’s exempt status. Some states issue project-specific certificates that the contractor must apply for before making purchases.
The detail most contractors miss: the exemption typically covers only materials that become part of the project. Your tools, consumable supplies, and equipment rentals remain taxable even on a fully exempt government job. If you purchased materials without claiming the exemption, some states allow you to take a credit for the sales tax you already paid, though the documentation requirements are strict.
Not every state extends exemptions this way. Some treat the contractor as the consumer regardless of the client’s tax status, meaning the government or nonprofit’s exemption doesn’t flow through to the contractor’s material purchases. Check with the state revenue department before assuming a client’s exempt status benefits you.
What Happens If You Get It Wrong
Sales and use tax mistakes compound. State penalties for late payment generally range from 0.5% to 5% of the unpaid tax per month, with caps that vary by state but often reach 25% to 35% of the total liability. Interest accrues on top of those penalties from the original due date, and the combined bill on a multi-year audit can dwarf the underlying tax.
Misusing a resale certificate carries its own penalties in many states, separate from the unpaid tax itself. Some states impose a flat percentage penalty on the tax that should have been paid on the improperly exempt purchase. These stack on top of the regular late-payment penalties and interest, so a contractor who routinely runs taxable purchases through a resale certificate faces a problem that gets expensive fast.
Every state also has criminal penalties for willful sales tax evasion, though these are typically reserved for egregious cases involving fraud or large dollar amounts. The more common risk is a civil audit that produces an assessment covering several years of underpaid tax, plus penalties and interest that together can exceed the original tax by a significant margin. Keeping clean records and understanding your tax posture before each project starts is far cheaper than sorting it out after an auditor arrives.