The US Tax Threshold You Cross Without Noticing
There is a particular kind of tax problem that does not announce itself. You do not file it late, because you did not know you had to file it. You do not collect it wrongly, because you did not know you had to collect it. You find out when a state writes to you, by which point the tax you should have collected has already left as margin you spent eighteen months ago.
What economic nexus actually says
Until 2018, a US state could generally only make you collect its sales tax if you had a physical presence there — an office, a warehouse, a person. South Dakota v. Wayfair replaced presence with activity. Sell enough into a state and you are its tax collector, whether or not you have ever been there.
For a Canadian business shipping into the US, or a seller whose marketplace stock sits in an American warehouse chosen by an algorithm, this is not a hypothetical.
It is not one threshold, and that is the trap
The number people remember is $100,000. It is a fine starting point and it is wrong often enough to matter. Some states add a transaction count. Some measure gross sales, some only taxable sales, some only retail. Some look at the current calendar year, some at the previous one.
So the same twelve months of revenue can create an obligation in one state and none in the state next door — and a business tracking a single national figure will be confident and wrong at the same time.
Marketplace sales are the confusing part
Where a marketplace facilitator collects and remits on your behalf — which Amazon does in every state requiring it — that tax is not yours to collect, and sellers reasonably conclude they are covered. Whether those sales still count toward YOUR threshold depends on the state. In some, marketplace revenue can push you over a line for your own direct sales without you ever handling a cent of the tax.
Crossing it should be a date in a calendar
Everything above is manageable and none of it is urgent — until it is both. The entire difference between a scheduled registration and an assessment letter is whether anybody was watching the running figure against the right test.
That is the argument for measuring it in the books rather than in a spreadsheet somebody updates when they remember. Thresholds also move, which is why the ones SeroBooks uses carry a review date; a threshold nobody is maintaining is worse than no threshold at all, because it is trusted.
See it in your own numbers.
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