Hello lovely community,

I have my first C Corporation client that was incorporated in Delaware, and registered as a foreign entity in several states. The corporation does business in a dozen of states but only registered in half of them because there is either no registrations requirement in those states, or the sales amount in those states doesn't exceed certain threshold. For income tax purposes, I am assuming that I need to apportioned the total sales for the year between all different states and file their state income tax returns, even for those that the corporation is not registered with, correct? 

Any further clarification on this topic would be highly appreciated.

Thanks