I just arrived to US because of a post-doc position in an IT company, under a J-1 visa (research scholar). I have been told by the company to fill W-4 form in. But, it seems that W-4 form must be filled in differently depending on my current status (resident alien or nonresident alien).
The rules to decide which is my status are here: http://www.irs.gov/publications/p519/ch01.html
Basically, it seems I need to pass the substantial presence test (see previous link) to determine whether I am a resident alien or not (I cannot meet the other criteria: green card test). At this moment, I definitely do not meet the substantial presence test, since I just arrived to US.
I understand, however, that I will need to file my first tax return on April 2014 (since I am going to start working next week, and my fiscal year will end on December 2013). At that moment, I believe I will actually meet the substantial presence test.
So, my question is: should I decide if I am a resident alien or not based on the date that I start working, or based on the date I will file my tax return?