How is the nexus threshold calculated — calendar year or trailing 12 months?

Most states use a calendar year measurement window, either the prior calendar year or the current calendar year, not a rolling 12-month period. A meaningful minority of states use a trailing 12-month lookback. The distinction matters: if your sales are growing, a trailing 12-month lookback catches threshold crossings faster than a calendar year window.

The two main approaches

Calendar year (majority of states): You cross the threshold if your sales into the state exceeded $100K (or 200 transactions) in either:

• The prior calendar year (January 1 – December 31), or
• The current calendar year (January 1 – present)

Under this approach, crossing the threshold mid-year in Year 1 means you start collecting in Year 1 (or at the start of Year 2 at the latest, depending on the state’s rules). You reset to zero on January 1 each year.

Trailing 12 months: Some states measure your sales over the most recent 12-month rolling period, regardless of where that period falls on the calendar. A crossing in July counts; a crossing in March counts. There’s no annual reset: the window moves continuously.

Which approach each state uses

Most states don’t publish a simple “calendar vs. trailing” label in their guidance, you have to read the statute. As a general rule:

• Prior calendar year or current calendar year: the majority of states, including California, Texas, Florida, New York, Illinois, and most others that adopted economic nexus after Wayfair (2018)
• Trailing 12 months: a meaningful minority, including Ohio (prior 12-month period), South Carolina, and some others

The SST (Streamlined Sales Tax) model statute uses a prior or current calendar year approach, so SST member states tend to follow that framework.

Because this changes by state and rules are updated, verify the specific state’s current statute rather than relying on a general rule. Your state’s Department of Revenue nexus or remote seller guidance page will specify the measurement period.

Why this matters in practice

Scenario 1 — Calendar year advantage: You crossed $100K in Texas in November of Year 1. If Texas uses a current-calendar-year trigger, you owe tax from the date you crossed. But after January 1 of Year 2, your counter resets to zero, if Year 2 sales stay under $100K, you may lose nexus.

Scenario 2 — Trailing 12-month pressure: You crossed $100K in Ohio in April of Year 1 (trailing 12 months). The clock doesn’t reset in January. You remain in nexus for as long as your rolling 12-month total stays above $100K. If sales dip below in a trailing window, you could lose nexus, but you need to track this continuously, not annually.

The practical rule for growing sellers

If your sales are growing, a trailing 12-month state will catch you faster than a calendar year state, you can cross the threshold mid-year based on sales from the past 12 months rather than waiting for the calendar year to accumulate.

The safest approach for mid-market sellers tracking multiple states:

1. Use a sales tax platform or nexus tracking tool that applies each state’s correct measurement window automatically
2. Run a threshold audit at least quarterly: especially if you’re approaching $100K in any state
3. Don’t assume calendar year for states you haven’t explicitly verified

Related: When do I have to start collecting sales tax in another state?