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. You will have to file a non resident MO state return and pay MO tax on the income earned there.. You will also file a CA full year resident return and calculate tax on ALL your income. CA will give you a credit, or partial credit, for the tax you pay MO. So, there will be little or no double taxation. Do the nonresident state return first.
