For federal tax it does not matter where you live during the entire year. But it does matter for the state tax. If you were going to file a state tax in NY as a part time residence, then you would need to file CA state tax as well. But since you didn't work and paid any state tax in CA, you may go head and file NY state tax claiming yourself as a full time residence. Some state deduct less tax if you claim yourself to be a part time residence. Do your math and find out which way you are going to get more refund.