Well, it is for everyone that uses the Georgian Calendar (which most people in the world do, at least for civil purposes). However, before the adoption and standardisation of this calendar there were many different “New Year’s,” and for those that use none-Georgian calendars there still are. Here’s a short run down:
March 25: Many European used this date (the Feast of Annunciation) as the start of their year, including England (until 1752).
Christmas: Many European nations used this as the start date of the year in the Middle Ages.
September 1: the Byzantine Empire used this as their New Year’s day.
February 8, 2016: This is the date of Chinese New Year, they use a lunisolar calendar system so their New Year’s moves around a bit.
October 2 (sundown) to October 4, 2016: This is when Rosh Hashanah happens in 2016, the Hebrew calendar is a lunar system.
Autumnal Equinox: This was when the year began on the French Republican/ Revolutionary Calendar used between 1793 and 1805. (If it was still used today the New Year’s day would be September 22).
Happy New Year’s Day! (if you are using the Georgian Calendar, if not Happy January!)
Info about the switch for the Julian to Georgian calendars: http://www.cree.name/genuki/dates.htm
General info: http://aa.usno.navy.mil/faq/docs/calendars.php
Chinese New Year: http://www.travelchinaguide.com/essential/holidays/spring-festival.htm
Byzantine Empire: http://grigam.narod.ru/kalend/kalen19.htm
Rosh Hashanah: http://www.chabad.org/holidays/jewishnewyear/template_cdo/aid/671869/jewish/When-is-Rosh-Hashanah-in-2014-2015-2016-and-2017.htm