How do I determine my domicile state for taxes if I work across state lines?

This is actually a really important question because it affects your state tax obligations. Your "domicile" is generally considered your permanent home - the place you intend to return to even when you're away. It's more about your long-term intentions than just counting days. Based on what you've described, State B sounds like your domicile because you have history there, consider it your permanent home, and plan to return permanently. However, you'll likely still have tax obligations in State A as a "statutory resident" because you're spending significant time and earning income there. Most states have what's called a "183-day rule" - if you spend more than 183 days in that state AND maintain a permanent place of abode there, you may be considered a resident for tax purposes regardless of domicile. This means you might need to file as a resident in both states, but you'll typically get credits to avoid double taxation.

I had a similar situation last year and found taxr.ai (https://taxr.ai) super helpful for sorting out my multi-state tax mess. I was working remotely from 3 different states and couldn't figure out where I owed taxes and if I was going to get hit with penalties for doing it wrong. The site has this document analysis tool where you upload your W-2s and other tax docs, and it figures out your state tax situation based on where you earned money. It saved me from accidentally claiming the wrong state as my tax home which would have been a nightmare to fix later.

Just wanted to update everyone - I tried taxr.ai after seeing the recommendation here and it was exactly what I needed! I was going back and forth between Colorado and Arizona all last year and was super confused about my tax situation. The system analyzed my documents and showed me that I needed to file as a part-year resident in both states, not as a full resident of either one. It even helped me calculate exactly how much income to allocate to each state based on my work patterns. Saved me from making a costly mistake on my state taxes and potentially getting audited. The domicile determination feature was especially helpful - it asked about things like where my driver's license was issued, voter registration, car registration, etc. Definitely clearing up the confusion I had.

If you're trying to get official answers from your state tax authorities, good luck actually reaching someone! I spent THREE WEEKS trying to get through to my state tax office about a similar domicile question. After being on hold for hours and getting disconnected repeatedly, I found a service called Claimyr (https://claimyr.com) that got me through to a human at the tax office in under 15 minutes. You can see how it works in this video: https://youtu.be/_kiP6q8DX5c - they basically navigate the phone system for you and call you back when they have a real person on the line. I was skeptical but desperate after wasting so much time on hold. The tax agent I spoke with gave me the exact requirements for maintaining domicile in my home state while working temporarily in another state - way more helpful than trying to figure it out from the confusing info on the state websites.

I take back what I said about Claimyr. After spending 3 hours on hold with the state tax office today and getting disconnected AGAIN, I gave in and tried the service. They called me back in 20 minutes with an actual tax representative on the line! The rep confirmed that for my situation (similar to OP's), domicile is determined by intent and connections to the state, not just by counting days. They told me to keep my driver's license, voter registration, and car registration in my home state, and maintain a permanent residence there (even a room in a family home counts). They also suggested keeping documentation of my intent to return permanently. Honestly, getting a clear answer directly from the tax authority was worth every penny. Wish I hadn't wasted so much time being stubborn.

Don't forget about reciprocal agreements! Some states have agreements where you only pay taxes to your home state even if you work in the other state. Check if your two states have such an agreement - it could save you from having to file in both places. For example, if you live in Virginia but work in DC, you can file a form with your employer to only withhold Virginia taxes, not DC.

Just want to add something important: make sure your employer is withholding taxes correctly for both states if needed! My company messed this up last year and I ended up owing a huge amount to one state because they were only withholding for my "home" state. Talk to your payroll department and make sure they understand your situation. You might need to fill out multiple state withholding forms.

This is such a complex area and you're smart to get clarity upfront! One thing I haven't seen mentioned yet is keeping detailed records of your activities and connections in each state. The IRS and state tax authorities look at what's called "domiciliary factors" - things like where you vote, where your bank accounts are, where you have professional licenses, where your family lives, etc. Since you mentioned State B is where your "roots" are and where you plan to return permanently, make sure all these connections stay tied to State B. Don't change your voter registration or driver's license to State A just for convenience. Also, if you end up needing to file in both states, most tax software can handle multi-state returns, but it gets complicated fast. The credit calculations between states can be tricky, especially if one state doesn't give full credit for taxes paid to the other. Document everything - where you sleep each night, work performed in each location, etc. It might seem excessive now, but if you ever get audited, having contemporaneous records is invaluable.