During the Middle Ages under the influence of the Catholic Church, many countries in western Europe moved the start of the year to one of several important Christian festivals – December 25 (the Nativity of Jesus), March 1, March 25 (the Annunciation), or even Easter. The Byzantine Empire began its numbered year on September 1.
In England, January 1 was celebrated as the New Year festival, but from the 12th century to 1752 the year in England began on March 25 (Lady Day). So, for example, the Parliamentary record notes the execution of Charles I as occurring on January 30, 1648, (as the year did not end until March 24), although modern histories adjust the start of the year to January 1 and record the execution as occurring in 1649.
Most western European countries changed the start of the year to January 1 before they adopted the Gregorian calendar. For example, Scotland changed the start of the Scottish New Year to January 1 in 1600. England, Ireland and the British colonies changed the start of the year to January 1 in 1752. Later that year in September, the Gregorian calendar was introduced throughout Britain and the British colonies. These two reforms were implemented by the Calendar (New Style) Act 1750.
January 1 became the official start of the year as follows: