British J-1 (Research scholar) VISA holder here. Moved to the US in August 2014. I have a question that pertains to a tax treaty exemption. The treaty states that I am exempt from federal and state/city taxes for two years if I stay in the US for under two years, otherwise I forfeit this treaty and I have to make a retroactive payment of due taxes. My question is, do the two years refer to calendar years from my date of entry (i.e. August 2016), or does it refer to tax years (i.e. end of 2015)? Also, if I have had taxes withheld, how would I be able to claim these taxes back from outside of the US? I assume my employer would forward me a W-2 to the UK and then I would complete the 1040NR and claim a tax treaty exemption?

Any advice would be greatly appreciated.