It’s unclear whether you are asking about 2019, 2020, or 2021. If we presume 2021, then how did your spouse file for 2019 and 2020?
Let’s review the basics in order. The first concept is domicile. A person‘s domicile is their true and permanent home, it is where they have the most significant social, legal, financial, and business ties. You can maintain a domicile in one location even if you are in another location for an extended period of time, so long as it is not your intention to permanently change your domicile. It sounds like whatever state you and your spouse currently live in is your domicile.
Next, we have to consider temporary residency. In this case, your spouse was a temporary or transient person in California for 2019 and 2021, but may have been considered a legal resident for tax purposes for 2020, even if he did not change his domicile. That is because California presumes that a person who spends nine months, or 270 days, in the state of California is a resident. Spending 4 to 5 days per month per week could easily add up to 271 or more days, although he would have to do the math on this.
Next, we address the question of how to file a tax return if you have a domicile or permanent residence in state A and temporarily work in state B. You always owe a full year resident tax return to the state of your domicile or permanent residence. You also owe a non-resident state income tax return to any state that you live or work in during the year. The non-resident return only reports income that is earned while living or working in that non-resident state. So your spouse is required to file a non-resident California return that reports the income that he earned while living or working in California, and an income tax return for his home state that reports all his worldwide income. His home state will give him a credit for taxes paid to California. In TurboTax, prepare the nonresident state first and then prepare the resident state last so that the credit flows correctly to your home state.
You can file a joint federal return along with a joint California state nonresident return and a joint state return for the state of your permanent residence. Because the California nonresident return will only report California source income, none of your income will be taxed in California even if you file a joint return.
For 2019 and 2021, your spouse is clearly a non-resident of California because of the 9 month rule. However, for 2020, your spouse might be considered a legal resident of California for tax purposes, even if he did not change his domicile. He could file a non-resident tax return to report his California source income, but there is a chance that California will insist that he was a state resident and assess tax on all his income, in which case you will have to fight with the FTB to prove that he was a non-resident.
