For federal tax purposes, whether or not taxpayers have community property and community income depends upon their domicile and the laws of the state where the domicile is located. (IRS Pub 555 – 3/2020, Pg 2).

The United States government offers criteria to help taxpayers determine where they are legally domiciled.

The determination of domicile for income tax purposes is essentially a question of federal law. Hence federal decisions and rulings on questions of domicile relating to one state are generally equally applicable to other states.

A taxpayer has only one domicile even though the taxpayer may have more than one residence. Domicile is a permanent legal home that a taxpayer intends to use for an indefinite or unlimited period, and to which the taxpayer intends to return. Domicile is generally a matter of intent based upon a taxpayer's actions. So there is no bright line definition of domicile and a taxpayer must be able to show factually that he or she intends a given place or state to be his or her permanent home. Time spent in one place doesn't always define the difference between a residence and a domicile. Some of the factors considered in determining domicile are:

The fact that a taxpayer is living in the U.S. under a visitor's visa doesn't exclude the intent necessary for U.S. domicile (May, (1939) 39 BTA 946, nonacq).

An intention by spouses living in a foreign country to move to a community property state, and their oral agreement that their present income will be community income, isn't sufficient to make the income community income (Hampton, (1962) 38 TC 131).