Post-Wayfair Sales Tax Compliance for E-Commerce Retailers

South Dakota v. Wayfair changed sales tax overnight in 2018. For seven years since, e-commerce retailers have been catching up with the reality that selling into a state can create a filing obligation without ever setting foot there. For a Boise apparel brand shipping to 40 states or a Salt Lake City DTC food seller doing volume through Shopify and Amazon, the compliance surface can quietly outgrow the accounting team.

The mechanics are not complicated. The trap is knowing when a threshold is crossed, which states have dropped their transaction count, and how marketplace facilitator laws change what the seller still owes. Getting registration timing wrong is expensive, both in back tax and in state penalty layers.

Wayfair in One Paragraph and Why It Still Matters

The Supreme Court ruled that a state can require sales tax collection from a remote seller without physical presence, as long as the state’s nexus threshold is not unduly burdensome. South Dakota’s original standard was $100,000 in sales or 200 separate transactions into the state in the current or prior calendar year. Almost every state with a sales tax adopted a version of that standard within two years. The threshold you crossed three states ago last quarter may have created a registration obligation you have not addressed.

The 45-State Threshold Map

Forty-five states plus the District of Columbia now enforce economic nexus. The remaining five (Alaska, Delaware, Montana, New Hampshire, Oregon) have no statewide sales tax, though Alaska has local jurisdictions that collect. Thresholds vary in three ways:

• Sales-only states: California and Texas ($500,000), New York ($500,000 plus 100 transactions), Tennessee ($100,000). Transaction counts do not apply.
• Dollar-or-transaction states: Utah keeps the original $100,000 or 200 transaction test. Idaho enforces $100,000 in sales alone (transactions removed).
• No-threshold jurisdictions: Some states impose nexus on the first dollar for specific product categories, notably digital goods and marketplace sales.

State thresholds change. A retailer who mapped nexus in 2022 should re-run the analysis annually against current sales data.

Marketplace Facilitator Laws vs. Direct Sellers

Marketplace facilitator laws shift the collection duty from the seller to the platform. If a Utah retailer sells $200,000 through Amazon and $60,000 through their own Shopify site into California, Amazon collects and remits on the $200,000; the retailer still owes on their direct sales if they cross the state’s threshold on those alone. States differ on whether marketplace sales count toward the seller’s threshold at all.

Some sellers register unnecessarily because they include marketplace-facilitated sales in their nexus math. Others miss registration because they exclude them from a state that requires the combined count. The state-by-state coordination table is worth a serious look before filing anything.

When Registration Actually Becomes Required

Registration is triggered on the day the threshold is crossed, not the year-end. Most states allow a grace period of 30 to 60 days from crossing to register and begin collecting. Late registration exposes the seller to back tax on transactions after the trigger date, plus penalties and interest.

A common mistake: waiting for the annual tax return to discover a state was crossed. By then, the exposure window may span 8 to 10 months, and the seller owes tax the customer was never charged.

Software Options: Avalara, TaxJar, Sovos

Three platforms dominate the mid-market compliance stack. Avalara is the deepest for complex product taxability and multi-jurisdiction filing. TaxJar (owned by Stripe) works well for retailers already on Stripe or Shopify with straightforward taxability. Sovos is common for larger sellers or those with strong ERP integration needs.

All three handle registration, calculation, filing, and remittance. Cost scales with transaction volume and jurisdiction count. For a retailer active in 20 or fewer states, monthly cost typically runs a few hundred dollars. For a seller in all 45, expect a monthly SaaS bill in the low four figures plus filing fees.

Idaho and Utah Rules for In-State Sellers

Idaho’s economic nexus threshold is $100,000 in gross sales into Idaho in the current or prior calendar year. Idaho does not require a transaction count. Utah maintains $100,000 in gross sales or 200 transactions. Both states are Streamlined Sales Tax members, which simplifies registration through the SST Registration System for sellers that qualify.

Multi-state sales tax was one of the largest hidden compliance loads to hit small e-commerce retailers in the last decade. The retail advisory team at Cooper Norman works with clients across Idaho and Utah to run a nexus study, prioritize registrations, and set up a filing cadence that does not overload the bookkeeping team. If you would like a review of your state footprint or software stack, our tax planning group is a good place to start.

This overview is general information, not tax advice for your specific business. Talk with a Cooper Norman advisor about how these rules apply to your operation.