The California Franchise Tax Board runs one of the most aggressive residency audit programs in the country. Surviving it requires documentation — precise, date-stamped, audit-ready documentation — not just an updated driver's license.

Most people who know about the Substantial Presence Test think they understand it. They've heard '183 days' and built their travel plans around that number. The IRS knows it too.

The 90/180 rule uses a rolling window, not a fixed calendar period. The 180-day window doesn't reset on a specific date. Most travelers get this wrong, and border officers know it.

If you're leaving California or New York for good, which state fights harder? Both have dedicated audit units and win large cases years later—but California is a domicile state while New York's statutory resident rules are a mechanical trap. Here's how the difference shapes what you document after you move.