When I input the information for Turbo Tax for the military edition, it asked how many days my son lived in CO and in CA. I filed (for him) both a CO return (with no taxes due) and a CA return, (with no taxes due and a return of the CA taxes he had withheld (only $13). My own accountant said it was correct to file both CO And CA returns, because my son's income was earned in CO, so he is required to file a CO tax return. He used an example of the SUPER BOWL, and said all the athletes had to file a separate tax return for the state where they played in the Super Bowl. If my son had owed taxes in CO (which he did NOT) those taxes would have appeared as a credit on his CA return. Turbo Tax automatically filed both state returns, so it was not difficult, but my accountant's explanation was helpful, so I thought I would pass this along.