The Feast of the Annunciation, or Lady Day, is a commemoration of the angel Gabriel’s visit to Mary to inform her she would bear the Son of God. It was noted with liturgy within churches, but historically was linked to the beginning of a new year.
Lady Day has been celebrated since the Middle Ages, and was known as a Quarter Day along with Midsummer, Michaelmas, and Christmas. A debt had to be paid by the next Quarter Day, and if accounts were not settled then a reckoning would be publicly recorded on that day. Lady Day also signified the start and end of long-term land leases, with the annual date of renewal being 25 March. It was a day of great upheaval, as all the travelling farmers would move from one farm to another on Lady Day.
At length it was the eve of Old Lady-Day, and the agricultural world was in a fever of mobility such as only occurs at that particular date of the year. It is a day of fulfilment; agreements for outdoor service during the ensuing year, entered into at Candlemas, are to be now carried out.Thomas Hardy, Tess of the D’Urbervilles
Until 1752, Lady Day was the first day of the new year, and fell on 25 March under the old-style Julian calendar. That meant new debts—including tax on monies earned, land, purchases, and anything else—would be accrued after those of the fourth quarter, which began after Christmas, were settled on Lady Day. In 1750 the calendar was advanced by eleven days to the Gregorian calendar we now use, meaning the transition to a new year moved to 5 April, and then two years later 1 January became the first day of the calendar year, though debts still followed the Quarter Days. The tax acts drawn up at the time to reflect this change stated that the tax year would run from 5 April, which is why the tax year in the United Kingdom starts on 6 April and still does to this day.
Lady Day is still noted on its original day, and though the calendar has changed, the influence of the day remains on the British economy. Tax returns must cover the period of 6 April to the following 5 April, as per the original Quarter Days year.