Data sources

Last updated October 2026.

State residency rules

Each state's summary is written in our own words from its income tax statute or regulation, cited on its rule page with a link to the state's tax agency. We review the summaries when states change their laws, but always confirm with the official source before you rely on one.

IRS Substantial Presence Test

The federal test follows Internal Revenue Code section 7701(b) and IRS guidance for aliens (Publication 519). See how the test works.

Map outlines

• US states, DC and territories: U.S. Census Bureau 2024 cartographic boundary files (1:500,000), public domain, simplified for fast lookups in your browser.
• Other countries: Natural Earth 1:50m admin-0 countries, public domain.

Simplified outlines can be off by up to a few hundred meters, more along complex coastlines. A point that falls just outside every outline (on a beach, a lake or a river border) is matched to the nearest state within 25 km or country within 40 km and labeled so you can check it. Disputed borders follow Natural Earth's default and don't imply any position.

How days are counted

• Any part of a day in a place counts as a day there, the approach most states take. A travel day counts for every place you were in.
• The first and last day of a stay both count.
• Days are calendar dates as you enter them. Photo dates use the camera's clock.
• Days in US territories and abroad don't count as US days for the federal test.
• Some states count differently, such as Maryland's 24-hour rule, Ohio's contact periods, and Virginia and DC, which measure how long you keep a home. Those differences are noted on each state's page.