Multistate Sales Tax Bookkeeping: The $100,000 Lines You Cross Without Knowing

Since South Dakota v. Wayfair (2018), physical presence no longer protects you. Every state with a sales tax — 45 plus DC — now requires remote sellers to register and collect once economic activity crosses that state’s line, usually $100,000 in sales or 200 transactions into the state over a measurement year (Sales Tax Compliance USA, Economic Nexus Thresholds By State, June 25, 2026). The compliance problem isn’t the rule itself; it’s that crossing happens silently inside ordinary growth, and your books are the only instrument that sees it coming.

This guide covers the 2026 threshold map, the marketplace-sales trap that catches even careful sellers, and the bookkeeping routine that turns nexus from a scare into a checklist item.

The 2026 Threshold Map

Most of the country converged on the South Dakota model — $100,000 or 200 transactions, whichever comes first, measured over the previous or current calendar year. But the exceptions are where businesses get hurt:

• Higher thresholds: California, Texas, and New York at $500,000; Alabama and Mississippi at $250,000. New York uniquely requires both $500,000 and 100 transactions.
• Both required: Connecticut demands $100,000 and 200 transactions — neither alone triggers nexus.
• No sales tax at all: Delaware, Montana, New Hampshire, Oregon. Alaska has no statewide tax but lets municipalities adopt the Remote Seller Commission’s $100,000 regime.
• The transaction prong is dying: South Dakota repealed it in 2023, Louisiana and Indiana followed, Wyoming and North Carolina in 2024, then Alaska (January 2025), Utah (July 2025), and Illinois (January 1, 2026) (TaxCloud state-by-state chart, June 7, 2026).

The Marketplace Trap

Here’s the scenario that burns careful sellers: you sell on Amazon and your own site. Amazon collects and remits sales tax on its sales — so you assume marketplace activity is handled. But in most states, marketplace sales still count toward your economic nexus threshold (TaxCloud, June 7, 2026). Your own-site volume plus your Amazon volume can cross a state’s line while your own-site share alone wouldn’t. You then owe registration and collection on your direct sales into that state — an obligation the marketplace never covered.

Two more measurement wrinkles worth coding into your tracking:

• Exempt sales can count. Several states include non-taxable sales toward the threshold, so “we don’t even charge tax there” isn’t a defense for not counting the revenue.
• Measurement periods differ — previous calendar year, current year, or trailing twelve months. The same growth pattern can trigger nexus in one state and miss in another.

What Your Books Owe You Monthly

Nexus monitoring is a bookkeeping function now, not a tax-season scramble:

1. Tag every sale by ship-to state at entry time — POS and ecommerce platforms can do this; verify they do.
2. Run a per-state revenue report monthly against your threshold tracker ($100k standard; $250k/$500k outliers).
3. Count transactions separately where the 200-prong still exists — low-ticket sellers cross it first.
4. Calendar registration deadlines by state, because they range from “next transaction” to “first day of the month after 90 days past crossing” (Sales Tax Institute economic nexus chart, retrieved August 23, 2026).
5. Reconcile collected versus remitted quarterly, separating marketplace-facilitated amounts from direct collections.

The expensive mistake isn’t failing to collect — it’s the lookback. Register late and states can assess tax you should have collected from customers who are long gone, converting your gross margin into their revenue. A $200/month monitoring habit insures against a five-figure retroactive bill; almost nothing else in your books has that asymmetry.

If You’ve Already Crossed a Line

Don’t register in panic order — register in deadline order:

1. List every state where you exceeded a threshold, with the crossing date from your reports.
2. Register immediately in states whose deadlines have passed — voluntary disclosure agreements (VDAs) can cap lookback windows where exposure is old and large.
3. Set collection rules in your platform per registered state before the next sale ships.
4. Backfile returns for interim periods; most first-time registrants get penalty abatement for asking.

A Web Works LLC ecommerce client crossed four state thresholds in one holiday quarter — growth they celebrated, compliance they hadn’t modeled. Because their books tagged ship-to state from day one, we produced exact crossing dates per state, registered within each state’s window, and closed the quarter with zero assessed penalties. The same scenario without those tags would have been archaeology: reconstructing twelve months of orders by hand during an audit inquiry. Ship-to tagging is cheap; its absence is not.

Frequently Asked Questions

What is economic nexus in simple terms?

Selling enough into a state creates a tax obligation there even with no office, staff, or inventory in it — usually $100,000 in sales or 200 transactions per year, measured on that state’s calendar.

Do marketplace sales count toward my nexus threshold?

Usually yes, even when Amazon or Etsy collects the tax itself. Marketplace volume stacks with your direct sales when states measure your activity, which can trigger registration duties on your direct channel alone.

Which states have different thresholds than $100,000?

California, Texas, and New York use $500,000 (New York also requires 100 transactions); Alabama and Mississippi use $250,000; Connecticut requires both $100,000 and 200 transactions together.

What should I do if I just realized I crossed a threshold months ago?

Register now rather than waiting — then ask about voluntary disclosure agreements for older periods. Deadlines and penalty exposure run from your crossing date, not your discovery date.

How does Canadian GST/HST differ from US multistate sales tax?

Canada runs one federal regime with clear thresholds and one registration — our companion guide covers it (GST/HST bookkeeping in Canada); the US system is fifty separate rulebooks, which is why monitoring lives in multistate sales tax bookkeeping stack. Both sit inside the broader client bookkeeping solutions framework.