In England, before 1752, the New Year started on 25 March, so for example the day after 24 March 1749 was 25 March 1750 and the day after 31 December 1750 was 1 January 1750. It can therefore appear that some people made their wills after they had died! The dates were also 11 days behind in this ‘Julian’ calendar system.
To change from the Julian calendar system to the one used now, the year 1751 was a short year of 282 days, running from 25 March to 31 December. The year 1752 began on 1 January in accordance with the Gregorian calendar. To align the new calendar in use in England to that in use on the continent, the calendar was also advanced by 11 days: Wednesday 2 September 1752 was followed by Thursday 14 September 1752. The year 1752 was thus a short year (355 days) as well.