State tax filing

There are residency rules that have been changed due to Covid-19, which I think apply to you since you have been working remotely since March 2020. Per the State of California, when determining your filing requirement and residency status for 2020 California personal income tax returns, you should consider circumstances related to COVID-19.

Usually, if you are physically present in California for at least nine months you are presumed to be a resident of California for purposes of the California personal income tax.

However, actions you took related to COVID-19 should be weighed when evaluating whether to file a California resident return. Your actions based on COVID-19 may establish facts and circumstances that support a determination of whether you are in (or out) of California for other than a temporary or transitory purpose. 

Please consider the following determining factors which might be relevant:

• When the individual entered California
• Whether the individual remained in California after the COVID-19 period (and if so, how long)
• Whether the individual remained in California throughout the COVID-19 period
• Whether the individual provided COVID-19-related services in California
• Whether the individual cared for an at-risk family member or friend

From the information given, you stated that you planned to go back to California once the office reopens. It sounds like this is a transitionary move due to Covid-19. In that case, you would still have to file a resident California return with all the income being allocated to California. 

The other factor to this is whether or not you paid Arizona state income tax. You would then have to file a nonresident return if so. Otherwise, it is not an Arizona source income because you would not have telecommuted from Arizona if Covid-19 did not occur. 

If my assumptions are incorrect, then yes, you would file part-year resident returns for both states. 

@tgaule