Domicile and residency are two separate legal tests for where a person owes tax: residency measures physical presence, typically counted in days, while domicile identifies someone’s one permanent, intended-forever home, a status that can outlast an actual move for years.
In plain terms
Residency is the mechanical test. Most US states run some version of a 183-day rule: count the nights physically present, cross the line, and the state’s income tax applies for the year, no judgment call involved. Domicile is the stickier test — wherever a person’s own actions show an intent to return to as a permanent base, from voter registration to where the family actually lives — and once established, it doesn’t end just because someone starts spending more nights elsewhere; it has to be affirmatively abandoned. The gap is where most state tax fights happen: a person can spend fewer than half the year in New York and still face its auditors, because domicile is judged by conduct, not by a calendar.
How it works
At the federal level, non-citizens face a bright-line residency rule: the IRS’s substantial presence test (26 U.S.C. § 7701(b)(3)) adds up all days present in the current year, plus one-third of days from the prior year, plus one-sixth of days from two years before that. Hit 183 under that weighted formula, and have spent at least 31 days in the US in the current year, and the person is a US tax resident for the year — a pure arithmetic test with no intent requirement.
Domicile has no such formula and is used mainly by US states rather than the federal government. A state revenue agency instead weighs where someone keeps their permanent home, where a spouse and children live, voter and vehicle registration, and where they return after every trip. California’s Franchise Tax Board, in its own guidance for residents, defines domicile as “the place where you voluntarily establish yourself and family, not merely for a special or limited purpose, but with a present intention of making it your true, fixed, permanent home.”
Because the two tests run on different logic, they can produce overlapping, even contradictory answers. It is entirely possible to be a day-count resident of one state while remaining domiciled, and therefore still taxable, in another that never saw the domicile legally given up.
The numbers
- IRS substantial presence test (unchanged for 2026): current-year days, plus 1/3 of prior-year days, plus 1/6 of days from two years earlier, must total 183 or more, with at least 31 days present in the current year.
- Common state-residency day count (New York, California, and most other high-tax states): 183 days physically present during the tax year.
- Domicile carries no day count at all — in principle, someone domiciled in a state who spends zero days there in a given year can still owe that state’s tax.
- California’s Franchise Tax Board updates its multi-factor domicile test annually; the 2025 edition of Publication 1031, used for 2026 filings, weighs family location, voter and vehicle registration, and professional licensing.
What people get wrong
People assume that spending fewer than 183 days in a state automatically makes them safe. It doesn’t — the day count governs residency, not domicile, and a state can still tax someone, or put them through an expensive audit, if their domicile never legally left, no matter how few nights they spent there. Moving your body is necessary but not sufficient; moving your domicile means a paper trail showing both departure and an intent not to return to the old home as permanent. It’s the exact gap that catches people who think they’ve “moved to Florida” the moment they buy a condo there and start counting days.
Related
Read more: Residency and Citizenship: Why the Wealthy Buy Options Across Borders · Taxes: How Wealth Is Structured and Preserved
See also: Non-dom · Expatriation / exit tax · Golden visa