The California Franchise Tax Board issued
guidance on the “stay-at-home” executive order
including the following question and response:
“Scenario 1: You work for an out-of-state employer
and receive a W-2 from them. You temporarily
relocate to California. Do you need to file a
California return and pay California income tax?
Answer: Yes. As a nonresident who relocates to
California for any portion of the year, you will have
California source income during the period of time
you performed services in California. You will need
to file a California Nonresident or Part-Year
Resident Income Tax Return (Form 540NR) return
to report the California sourced portion of your
compensation. One way to calculate the portion of
your income that is California sourced is to multiply
your total amount of income for the year by a ratio of
your total number of days performing services in
California over your total number of days performing
services worldwide.
Reference: https://www.hodgsonruss.com/assets/htmldocuments/Telecommuting_5.22.20.pdf
NY will give you a credit, or partial credit, for tax paid to CA
