State tax is where a lot of otherwise-simple returns get complicated. Move mid-year, take a remote job for an out-of-state employer, or own a rental across a border, and you can suddenly owe returns in more than one state — each with its own rules about who counts as a resident and what income it can tax.
Residency is not the same as where you sleep
States look at two ideas. Domicile is your true, permanent home — the place you intend to return to. Statutory residency is a mechanical test: many states will treat you as a resident if you keep a permanent place to live there and spend more than a set number of days (often 183) in the state, even if your domicile is elsewhere. It is entirely possible to be taxed as a resident by two states at once if you are not careful.
Moving mid-year
In the year you move, you generally file a part-year resident return in each state, splitting income based on when you earned it. The mechanics matter: the date you change domicile, where your income was earned on each side of the move, and how each state treats items like capital gains or a year-end bonus.
Remote work and the "convenience" rule
The default rule is that you owe tax where the work is physically performed. But a handful of states — New York most notably — apply a convenience of the employer rule: if your job is based in their state and you work remotely for your own convenience rather than your employer's necessity, they may still tax that income. Take a remote role for a New York employer while living elsewhere and you can end up filing there too.
The credit that usually — but not always — fixes it
Your resident state typically gives a credit for taxes paid to other states, which prevents most double taxation. "Most" is the operative word: the credit is generally limited to your resident state's rate on that income, so if you worked in a higher-tax state, the credit may not cover the full bill. Convenience-rule situations can leave gaps too.
Equity compensation adds another wrinkle: RSUs and options are often sourced to the state where you worked during the vesting period — so stock that vests after you move can still be partly taxable by your old state.
The bottom line: tell your CPA before you move or take a cross-border remote job, not at filing time. State sourcing is determined by the facts during the year — day counts, work location, the timing of a move — and those cannot be re-created in April.
This article is general information, not tax, legal, or accounting advice, and reading it does not create a CPA-client relationship. Tax rules change and depend on your specific facts — please consult a qualified professional about your situation before acting.