I agree with both Jan and Megan- every witch is free to choose when they feel the New Year begins, and it does indeed differ from one witch to the next!
For me personally, I think the longer you study and connect with the cycle of the seasons, the harder it is to find the “beginning and end of a circle” so-to-say. I believe that many of the points on the Wheel of the Year can make a solid claim for why they should mark the start of a new beginning 
@Amaris_Bane shared a great poll not too long ago asking the coven when they choose to celebrate the new year in their personal practice. The poll and the comments are very interesting- I recommend checking it out! 
Blessed be! 