Today, 1 January was regarded as New Year's Day and celebrated as such, but from the 12th century until 1751 the legal year in England began on 25 March (Lady Day). So, for example, the Parliamentary record lists the execution of Charles I on 30 January as occurring in 1648 (as the year did not end until 24 March), although later histories adjust the start of the year to 1 January and record the execution as occurring in 1649.
Most Western European countries changed the start of the year to 1 January before they adopted the Gregorian calendar. For example, Scotland changed the start of the Scottish New Year to 1 January in 1600 (making 1599 a rather short year). England, Ireland and the British colonies changed the start of the year to 1 January in 1752 (so 1751 was a short year with only 282 days). Later in 1752 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.
It is important to keep these dates in mind if you have been fortunate enough to trace you family back past 1752, as the calendar used at the time will skew the year in which events, particularly baptisms, marriages and burials, were recorded if they took place between 1 January and 25 March.
Consider the example of the baptism records above. It records the baptism of Susannah, daughter of John Dixon and Susannah his wife on July 8, 1722. It also records the baptism of Anna, daughter of John Dixon and Susannah his wife on March 17, 1722. This is going to look very odd on a modern timeline, if you don't take into account that in the modern calendar, Anna is baptised on March 17, 1723 - approximately 8.5 months after sister Susannah and not 3.5 months before her.