In England, Lady Day was New Year's Day (i.e. the new year began on 25 March) from 1155 until 1752, when the Gregorian calendar was adopted and with it the first of January as the official start of the year.
A vestige of this remains in the United Kingdom's tax year, which starts on 6 April, or "Old Lady Day", i.e., Lady Day adjusted for the 11 "lost days" of the calendar change (making it 5 April) and then moved on a day to 6 April after 1800 (but not moved on again after 1900 for some reason).
Until this change Lady Day had been used as the start of the legal year.
This should be distinguished from the liturgical and historical year.
It appears that in England and Wales, from at least the late 14th century, New Year's Day was celebrated on 1 January as part of Yule.

As a year-end and quarter-day that conveniently did not fall within or between the seasons for ploughing and harvesting, Lady Day was a traditional day on which year-long contracts between landowners and tenant farmers would begin and end in England and nearby lands (although there were regional variations).
Farmers' time of "entry" into new farms and onto new fields was often this day.
As a result, farming families who were changing farms would travel from the old farm to the new one on Lady Day.
In 1752 England finally followed western Europe in switching to the Gregorian calendar from the Julian calendar.
The Julian lagged 11 days behind the Gregorian, and hence 25 March in the Old Style calendar became 5 (after 1800, 6) April ("Old Lady Day"), which assumed the role of fiscal and contractual year-beginning. (
The date is significant in some of the works of Thomas Hardy, such as Tess of the d'Urbervilles and Far from the Madding Crowd, and is discussed in his 1884 essay "The Dorset Farm Labourer").

The logic of using Lady Day as the start of the year is that it roughly coincides with Equinox (when the length of day and night is equal); many ancient cultures still use this time as the start of the new year, for example, the Iranian new year and the ecclesiastical Hebrew new year.

In Ireland, however, Lady's Day means 15 August, the Feast of the Assumption of Mary, and is a day when fairs are celebrated in many country towns.
In England, Lady Day was New Year's Day (i.e. the new year began on 25 March) from 1155 until 1752, when the Gregorian calendar was adopted and with it the first of January as the official start of the year. A vestige of this remains in the United Kingdom's tax year, which starts on 6 April, or "Old Lady Day", i.e., Lady Day adjusted for the 11 "lost days" of the calendar change (making it 5 April) and then moved on a day to 6 April after 1800 (but not moved on again after 1900 for some reason). Until this change Lady Day had been used as the start of the legal year. This should be distinguished from the liturgical and historical year. It appears that in England and Wales, from at least the late 14th century, New Year's Day was celebrated on 1 January as part of Yule.
As a year-end and quarter-day that conveniently did not fall within or between the seasons for ploughing and harvesting, Lady Day was a traditional day on which year-long contracts between landowners and tenant farmers would begin and end in England and nearby lands (although there were regional variations). Farmers' time of "entry" into new farms and onto new fields was often this day. As a result, farming families who were changing farms would travel from the old farm to the new one on Lady Day. In 1752 England finally followed western Europe in switching to the Gregorian calendar from the Julian calendar. The Julian lagged 11 days behind the Gregorian, and hence 25 March in the Old Style calendar became 5 (after 1800, 6) April ("Old Lady Day"), which assumed the role of fiscal and contractual year-beginning. (The date is significant in some of the works of Thomas Hardy, such as Tess of the d'Urbervilles and Far from the Madding Crowd, and is discussed in his 1884 essay "The Dorset Farm Labourer").
The logic of using Lady Day as the start of the year is that it roughly coincides with Equinox (when the length of day and night is equal); many ancient cultures still use this time as the start of the new year, for example, the Iranian new year and the ecclesiastical Hebrew new year.
In Ireland, however, Lady's Day means 15 August, the Feast of the Assumption of Mary, and is a day when fairs are celebrated in many country towns.
Lady Day