@TWSinCA
In general, a person must file a resident income tax return in the state of their permanent home that reports and pays income tax on all their worldwide income, no matter where they were living or performing the work at the time. If they performed work in another state, they also file a nonresident return for that state that only reports and pays income tax on income from that state. Their home state will almost always give them a credit for taxes paid to another state, up to, but not over the amount of their in-state tax. For example, if the tax in New York on this income is $300 and the California tax on this part of his income is $400, he will pay $300 to New York State and California will give him a $300 credit, so he pays a net $100 to California. If the New York income tax on this income is $300 and the California income tax is $200, he would pay $300 to New York State and get a $200 offsetting credit in California.
To make this work in TurboTax, you have to prepare the non-resident return first. Then, the tax and credit will flow to the resident state return. Make sure that you do not indicate that your son was a resident of New York State. If he was temporarily working in New York, but his permanent home is in California, then he is only a resident of California, even if the temporary work lasted a long time. Also note that you have to manually allocate all your son’s sources of income between New York and California. TurboTax can’t gas for you. If your son had wages from another job, or investment income, or other taxable income, you will have to be sure to tell TurboTax in the New York State module that those items of income are not from a New York source.
Your son is not subject to New York City income tax, because only residents are subject to city income tax, and temporary workers whose permanent residence is elsewhere do not pay city income tax.
