@wasoki - The original post named MI & FL. I'll use those as example.
If you lived and worked in MI, prior to retiring, and now split your time between FL & MI, for tax purposes, you are still a full year resident of MI and will MI tax on all your income.
Let's say the 2nd state (unlike FL) also has an income tax (I'll use SC as an example). You are still a full year MI resident and only pay MI tax, unless you do something specific to change your residence (car & driver licenses and voter registration).
It also depends on the specific states. NY in particular has strict residency rules. If you maintain a residence in NY, you will continue to pay NY tax, even if you change your voter registration, etc. Check your state(s) tax agency web site for specific residency rules.
