I lived in New York State (NYC to be exact) from January 2018 to June 2018, at which point I moved to Texas. However, I continued to be employed by my NYS-based employer until August 2018. Regarding allocation of income, I'm assuming I would report the income I earned from January to June as "New York resident" income and the income I earned from July to August as "nonresident income"? The potential difference in my refund is quite large depending on how I allocate my income, so any insight into this would be much appreciated. Thank you!
Generally, you will have to file a non-resident tax return for income you received while working in a state that is different from where you live. Therefore, you are correct that you'll file a resident New York return for Jan 2018 to June 2018, and a non-resident New York state return for July 2018 to August 2018. Plus, you will need to file a resident Texas state return for the time where you are a resident of that state.
To ensure accurate calculations, TurboTax strongly recommends preparing your nonresident state return before you prepare your resident state return. Here's additional info on how to file a nonresident state return:
https://ttlc.intuit.com/replies/3302052