In 2016, I was a California resident from January 1 to May 30 and became resident of Florida from May 31 till the end of the year. How should I file my state tax returns? Do I need to file for both California and Florida? Does tax calculation for a given state rely on the duration of the residency in that state or income earned while lived in that state (or is it both)?

Thanks!

In 2016, I was a California resident from January 1 to May 30 and became resident of Florida from May 31 till the end of the year. How should I file my state tax returns? ======>Since there is no state income tax in Fl state , you only need to file your CA return ads a part year resident of CA; on your part year CA return , you need o report only CA source income and other income that you earned as a CA resident.

Do I need to file for both California and Florida? ===>

As mentioned above.
Does tax calculation for a given state rely on the duration of the residency in that state or income earned while lived in that state (or is it both)?=>>Correct; you must report your CA source income that you earned from Jan 1-May 30 2016 on your CA part year return. No Fl return is needed since there is no state income tax in Fl state.