I reside in California and had an 3 month internship in Massachusetts. I earned $18,000 there and tax was withheld. Do I have to file both MA and CA state taxes?
Yes. Income earned while working in MA is taxable by MA, and also must be reported to CA as you are a CA resident. (But CA should give you a credit for tax paid to MA.) Complete the MA non-resident tax return first, then the CA return.
