When you move from one state to another during the year, your federal return does not change, but your state returns do. In most cases you file a part year resident return in each state, and each state taxes the income that belongs to the part of the year you lived there, plus any income sourced to it afterwards.
The date you moved is the dividing line, and it needs evidence behind it.
The belief that causes the trouble
The first thing people get wrong is assuming that the state they lived in on December 31 taxes the whole year. It does not. The new state taxes you from the day you became its resident, and the old state usually still expects a return for the months before.
Skipping the old state’s return is the common version of this mistake. Its payroll records show wages paid while you lived there, and a missing return is what eventually produces a letter.
What a part year return actually does
A part year resident return splits the year in two. For the months you were a resident, the state generally taxes all of your income, wherever it came from. For the months after you left, it taxes only income sourced to that state, such as wages for work physically done there or rent from property there.
The mirror applies in the new state. It taxes everything from your residency date onward, and it may tax income sourced to it before you arrived.
Many states compute the tax as if you were a full year resident and then prorate it by the share of income that belongs to them. The mechanics differ from state to state, which is why the forms differ. The principle does not.
Where both states claim the same income, a credit usually prevents paying twice. That credit is its own subject, and it depends on both returns being filed.
What decides the move date
The move date is decided by evidence, not by the day the truck arrived or by what you remember.
The records that carry weight are the ones a state would ask for: the lease start or closing date on the new home, the sale or end of lease on the old one, the date your driver’s license and vehicle registration changed, voter registration, and where your children go to school. A move with the old address still on your bank statements, your license and your voter record is a move the old state can dispute.
States look at where your life is, not where you say it is. The cleaner the break on paper, the shorter that conversation.
Income that is hardest to split
Wages paid on a regular schedule are straightforward: each paycheck falls on one side of the date. The difficulty is income that does not arrive on a date.
A bonus earned in one state and paid in the next. Where it was earned can matter more than when it was paid, and states do not all treat it the same way.
Stock that vests after the move. Equity compensation is often allocated across the states you worked in during the vesting period, not to the state you lived in on the vesting date. Your W-2 may already split it, or may not.
Remote work for an employer in the old state. If you keep working for the same employer after moving, the old state may still see its own payroll address on your W-2. Whether it can tax that work depends on its rules, and some states tax work for an employer based there even when it is done elsewhere.
Each of these is worth identifying before the return is prepared, not discovered while preparing it.
Moving expenses are no longer deductible for most people
Most people can no longer deduct the cost of moving on their federal return. The deduction is limited to members of the Armed Forces on active duty moving under military orders, and, from 2026, to employees and new appointees of the intelligence community. Some states have their own rules, so the state return may differ.
What to do before a year end move
If you are moving in the last months of the year, a few steps now prevent most of the work later.
- Tell your employer’s payroll team the date you move, on the day, so state withholding switches then. If it is updated at year end instead, the W-2 reports the whole year to the wrong state and the refund from the old state can take months.
- Change your license, registration and voter record promptly, and keep proof of the dates.
- Keep the closing statement or lease for both homes.
- Note any bonus, vesting or one off payment expected around the move, and when it was earned.
- If you have income outside wages, look again at your quarterly estimated payments, since the new state may expect them too.
A move is also a reasonable time to check whether the new state’s return will need anything the old one did not. Preparing both part year returns together, from one set of dates, is part of an individual return.