It depends on whether these were permanent or temporary residencies.
If they were permanent residencies, but something came up and you decided to move, then you would be a part-year resident of California and a part-year resident of Washington D.C.
File part-year tax returns for both states.
You said you spent three months in CA and five months in DC, so you would also be a part-year resident of someplace else for the other four months.
If one of your stays was temporary, such as attending school or taking a limited job assignment, and you maintained a permanent home in CA or DC, then you would be a full-year resident of your permanent state and a non-resident of the other state.
You would file a full-year resident return for your permanent state and a non-resident return for your temporary state. Your permanent state will give you credit for taxes paid to your temporary state.
Thanks Ernie. Confirming both CA and DC were permanent residencies and I was temporarily overseas for the time in between. Do I need to file a part year tax return for DC if I didn't work/earn any income?
"...I was temporarily overseas for the time in between..."
CA regards you as a resident until you establish your domicile in the "new" state.
From your description, it sounds like you did not establish your DC domicile until after your trip to Europe.
Therefore it's more accurate to say that you were a tax resident of CA for 7 months and of DC for 5 months, which means that any income you had during that 7 months would be taxable by CA.
For CA's rules on this, see Change of Domicile on page 10 of this CA tax publication:
https://www.ftb.ca.gov/forms/2021/2021-1031-publication.pdf
In TurboTax, you would indicate DC as your State of Residence, and indicate that you also lived in CA during the year.
Thanks Tom, appreciate the additional clarity.
Based on the CA tax publication you shared, it would appear that I would be considered a CA tax resident for only the first 3 months given we physically moved out of our 'prior domicile' in March, shipped all our belongings to DC and intended on moving to DC after our stint in Australia.
The one question remaining is whether I need to file a tax return in DC if I didn't work/earn any income for the remainder of the year?
"...it would appear that I would be considered a CA tax resident for only the first 3 months..."
I'm not sure that the California FTB will agree, given that one of their 3 criteria for Change of Domicile is "Physically moving to and residing in the new locality."