Sales Tax Basics for Online Sellers: Rates, Nexus and the Checkout Total

By the BusinessLipTools editorial desk · Last updated 12 October 2026 · 4 min read

Businesses arriving from VAT or GST countries meet US sales tax and experience a specific shock: there is no “the rate”. There are state rates, county rates, city rates and special-district rates, stacked on a single purchase, varying by the address the goods are delivered to — thousands of possible combinations, administered by jurisdictions that do not share one rulebook. The tax is also structurally different: it is charged once, at the final sale to the consumer, with no chain of credits behind it.

This article gives the working model an online seller needs: how the layers combine, the concept — nexus — that decides where you must collect at all, and why the destination of the goods usually controls the rate. It is a general orientation, not state-by-state guidance; the compliance details belong to your marketplace settings, your tax software or your adviser. The model, however, travels.

The good news hidden in the complexity is that the checkout arithmetic is simple. Everything difficult about sales tax happens before the calculation; the calculation itself is one addition and one multiplication.

How the layers stack

A typical taxable purchase might carry a state rate of 6%, a county rate of 1%, a city rate of 1.5% and a transit district rate of 0.25%. These are charged together, on the same pre-tax price, so the combined rate is their sum — 8.75% — and the tax on a 250 order is 21.88, for a checkout total of 271.88. Where each layer is charged on the same base, adding the rates is correct; the jurisdictions have divided the total between themselves by agreement, and your job is the combined figure and a record of its parts.

What varies bewilderingly is everything around that sum: which products are taxable at all (groceries, clothing and digital goods are treated differently from state to state, sometimes with price thresholds per item), whether shipping is taxed, and when exemptions apply. A seller's systems must therefore resolve three questions per order — is this item taxable in this state, at what combined rate, on which base — and only the middle one is arithmetic.

Nexus: the obligation follows your footprint

A seller does not owe collection everywhere by default. The duty arises from nexus — a sufficient connection with a state. Physical presence is the classic form: an office, a warehouse, inventory stored in a state's fulfilment centres, sometimes even regular in-person selling. On top of that, most states now operate economic nexus: cross a threshold of sales into the state — commonly measured in dollars, in some places also in transaction count — and the duty to register, collect and remit switches on, even with no physical presence at all.

The practical trap is that inventory creates nexus silently. A seller who places stock with a national fulfilment network may have inventory in a dozen states before selling meaningfully in any of them, and each placement is potentially a registration duty. Marketplace facilitator laws shift collection for sales made through large platforms to the platform itself — a genuine simplification — but a seller's own website sales stand outside that shelter. Knowing where your stock sleeps and where your sales are heading is not tax trivia; it is the map of your obligations.

Destination sourcing and the delivered price

Most states source the sale to where the buyer receives the goods — destination sourcing — so the rate is the customer's address's combined rate, not yours. A handful of states use origin sourcing for in-state sales, applying the seller's location rate instead. The consequence for quoting is that a delivered price cannot be finalised until the destination is known: the same 250 product totals differently in two neighbouring counties, let alone two states.

This shapes how honest sellers quote. “Plus tax” with the calculation performed at checkout on the delivery address is the standard pattern; advertising a tax-inclusive delivered price nationally is close to impossible without absorbing variable tax into margin. It also shapes record-keeping: the audit trail a state wants is per-order — item, destination, rate applied, tax collected — so the breakdown by jurisdiction must exist in your records from the first sale, because reconstructing it from bank totals years later is an excavation nobody enjoys.

Staying organised without drowning

The workable routine for a small seller has four parts. Know your nexus map: where stock sits, where you have presence, and which economic thresholds you are approaching — reviewed on a schedule, because thresholds are crossed by growth, not by decisions. Configure your channels: marketplace collection where the platform is the facilitator, and a tax calculation service or carefully maintained rate tables on your own store. Keep the per-order breakdown; storage is cheap and regret is specific.

And calendar the remittance: collected tax is not revenue, and the classic small-seller failure is spending it as if it were, then meeting the filing deadline with an empty account. Hold collected tax in a separate sweep, mentally or literally, from the day it arrives. Sales tax done well is boring — a map, a setting, a habit. Its failures are never arithmetic; they are always organisational, and they are almost all preventable by the four habits above.

Mistakes to avoid

• Quoting one “US sales tax rate” — no such thing exists; the rate is a property of the destination address.
• Placing inventory with a fulfilment network without realising each storage state can create nexus and a registration duty.
• Treating marketplace collection as covering your own website's sales — facilitator rules apply to the marketplace's sales only.
• Spending collected tax as working capital and meeting the remittance deadline with nothing set aside.

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