In most states, contractors do pay sales tax on the materials they buy for a job, because the state treats the contractor as the final consumer of those materials rather than a reseller. Tax is paid to the supplier at purchase, folded into the bid, and never appears as a separate line on the client’s invoice. But that default flips in specific situations, and knowing when it flips is the difference between pricing a job correctly and either overpaying tax or illegally collecting it from a client. Five states have no general sales tax at all: Alaska, Delaware, Montana, New Hampshire, and Oregon. Everywhere else, the rules turn on one question.
Consumer or Retailer: The Question That Decides Everything
When you buy lumber, pipe, or wiring for a project, are you the end user of that material or reselling it to your client? The answer determines where tax gets collected and on what dollar amount.
If you’re the consumer, you pay sales tax directly to the supplier at purchase. The tax applies to whatever you paid. Your invoice to the client doesn’t show a separate sales tax line because the tax was already baked into your costs. You can fold that tax into your overall price, but you can’t break it out on the client’s bill as if you were collecting it for the state.
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 up materials, the tax the client pays is calculated on that higher price. A contractor who buys $1,000 of lumber and marks it up to $1,200 collects tax on the $1,200 rather than the $1,000. In a state with a 6% rate, that means the client pays $72 instead of the $60 the contractor would have paid as a consumer.
Getting this wrong in either direction creates problems. Pay tax as a consumer when you should be collecting as a retailer, and you’ve overpaid. Collect tax as a retailer when the state considers you a consumer, and you’ve charged your client a tax you had no authority to collect, which some states treat as a serious violation.
How Your Contract Type Decides Your Role
The single biggest factor in whether you’re a consumer or retailer is how your contract is structured. Two contractors on the same street, using the same materials, can end up with opposite tax obligations based on how their agreements are written.
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 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 the client any additional sales tax.
Price your bid to account for the tax you’ll pay on materials. Contractors who forget end up absorbing it out of their margin. And if you skip paying tax to your suppliers under a lump-sum contract, the state will come looking for it at audit.
Time-and-Materials Contracts
A time-and-materials contract bills the client separately for labor and materials. In states that recognize the distinction, that separation can shift your role to 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 an 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. Ambiguous language can lead the state to reclassify the contract and treat you as the consumer.
Non-Separated Contracts
Non-separated contracts are hybrids that 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 Can Override the Contract
Even when a contract is clearly structured, the type of work can override the contract-based rules. Most states automatically classify a contractor performing a permanent real property improvement as the consumer of the materials, regardless of contract language.
A real property improvement means permanently attaching materials to a building or land so they become part of the real estate. Pouring a concrete 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 it before a project starts is worth the time.
Tools, Equipment, and Consumables Are Always Taxable to You
Here’s a rule that catches newer contractors off guard. Your tools, equipment, and consumable supplies are taxable to you no matter what type 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.
Items like scaffolding, safety equipment, sandpaper, welding gas, and thread-cutting oil are consumed by your business, not by the client’s project. You owe sales or use tax on every one of those purchases. The same applies to rentals of heavy equipment like excavators and boom lifts; in most states, renting tangible personal property is taxable, with tax calculated on the rental payments.
This matters most during audits. 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.
Is Construction Labor Taxable?
Most states do not tax 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 clients: they pay sales tax only on materials, not on the total project cost including labor.
A few states take a broader approach and tax services, including construction labor. Arizona and New Mexico are the most prominent examples, though the specific rules and rates differ. In those states, 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 taxable. The labor distinction only matters when materials and labor are billed separately.
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 for one.
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 usually want updated certificates periodically.
Not every state lets contractors use resale certificates. The Multistate Tax Commission’s uniform resale certificate, which is accepted across many states, 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. Using a resale certificate in a state that doesn’t permit it for contractors is a fast path to audit trouble.1Multistate Tax Commission. Uniform Sales and Use Tax Resale Certificate — Multijurisdiction
When Purchased Materials Get Diverted
A common compliance trap: you buy materials tax-free with a resale certificate and then use them yourself instead of reselling them. Leftover materials from a project get used to fix up your own office, or a project’s contract type changes after purchasing has already started. When materials bought for resale end up being consumed, 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.
Record Retention
Keep your resale certificates, purchase invoices, and sales tax returns longer than you think you need to. 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. If a supplier gets audited and can’t produce your certificate, the tax liability may shift to them, which tends to end the business relationship quickly.
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, 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. Any savings disappear if you’re properly self-assessing use tax, which is exactly the point. States designed use tax to keep 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 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 you have to apply for before making purchases.
The detail most contractors miss is that 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. And if you purchased materials without claiming the exemption, some states allow 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 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 It Costs to Get It Wrong
Sales and use tax mistakes compound quickly. 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 compounding problem that gets expensive fast.
Every state also has criminal penalties for willful sales tax evasion, though those are typically reserved for egregious cases involving fraud or large dollar amounts. The more common risk is a civil audit that results in an assessment covering several years of underpaid tax, plus penalties and interest that together can exceed the original tax by a significant margin. Understanding your tax posture before each project starts is far cheaper than sorting it out after an auditor arrives.