New Year's Day is observed on January 1, the first day of the year on the modern Gregorian calendar as well as the Julian calendar.

In pre-Christian Rome under the Julian calendar, the day was dedicated to Janus, god of gateways and beginnings, for whom January is also named. As a date in the Gregorian calendar of Christendom, New Year's Day liturgically marked the Feast of the Naming and Circumcision of Jesus, which is still observed as such in the Anglican Church and Lutheran Church.