The general rule is: your report all your income on your home state return, even the income earned out of state. You file a non-resident state return for the state you worked in and pay tax to that state. Your home state will give you a credit, or partial credit, for what you paid the non-resident state. He will have to file a non resident ID state return and pay ID tax on the income earned there.. He will also file a CA full year resident return and calculate tax on ALL his income. CA will give him a credit, or partial credit, for the tax he paid to ID. So, there will be little or no double taxation, but you have the cost and hassle of filing two state returns. Do the nonresident state return first.
