Hi, if I'm a resident of Washington state but currently live and work in San Francisco, CA, do I have to: 1. Become a California resident? 2. How would I file taxes?

[Hal_Al]

What do you think  makes you a WA resident?

 If live and work in CA, you are a CA resident and file a CA resident state tax return.  

If for some reason, you do qualify as a WA resident, you file a non-resident CA return and pay tax on your CA income.

[TomD8]

Whether you're a CA resident or not for tax purposes isn't up to you; it's determined by California tax law.

Even if you still maintain a home in Washington, California may still consider you a resident for tax purposes.  You can read CA's rules on determining residency here: https://www.ftb.ca.gov/forms/2018/18_1031.pdf

Regardless of whether you are a resident or non-resident of CA, CA can tax any income you have from work actually performed within CA.

The difference is that, if you are a CA resident, CA can tax ALL your income.  If you are a CA non-resident, CA can only tax income you earn in CA. 

[kaseythua]

@TomD8 thanks Tom!