Sales tax nexus is the connection between a business and a state significant enough that the state can require the business to collect and remit sales tax there, whether from having a physical presence or, increasingly, just enough sales volume.
Since a 2018 Supreme Court decision (South Dakota v. Wayfair), most states can establish nexus purely from sales volume or transaction count in that state, even with zero physical presence there. A company selling a taxable product or service across many states can trigger nexus, and a collection obligation, in states it has never set foot in.
This mostly affects companies selling taxable physical goods or certain services; a lot of SaaS and digital products are exempt in many states, though the rules vary state by state and change often enough that it's worth checking rather than assuming. Ignoring nexus doesn't make the obligation go away. It just means the liability quietly accumulates until a state notices.
Prepared by the same team that keeps your books, with credits you may already be owed caught along the way. Built by founders, investors, CPAs and startup people.