Each U.S. state has its own rules on what constitutes economic nexus, which can vary considerably.

Sales threshold: Economic nexus can be triggered by making a certain value of sales in a state during a given time period. Some states also have a trigger based on the number of transactions. A few states require that both triggers are met before the nexus is created.

Reference period: Most states look at the calendar year when determining whether the economic nexus threshold has been reached (e.g. January 1, 2025 to December 31, 2025). However, some states have different reference periods for determining nexus.

Transactions made through a registered marketplace facilitator excluded: To calculate nexus, some states allow sellers to exclude any sales made through a registered marketplace facilitator (e.g. Amazon, Ebay, a marketplace facilitator registered for sales tax who calculates, collects, and remits sales tax on the seller’s behalf).

Most states however require that sellers include both sales made directly to customers and sales made to customers through a marketplace facilitator when performing a nexus calculation.

Transactions made to a reseller excluded: Some states allow sellers to exclude sales made to resellers when performing a nexus calculation. As a general rule, sales made to resellers holding a valid exemption certificate are not subject to sales tax.

Limited to certain transaction types: Some states allow sellers to exclude certain types of sales when performing a nexus calculation, for example, non-taxable sales or sales of anything other than tangible personal property (TPP).

This means other types of transactions, such as services, digital products, or intangible goods (like software downloads, subscriptions, etc.), do not count toward the threshold calculation, unless specifically mentioned by the state's tax laws.