As we enter a new tax year, a common thought is "why does it start on the 6th April?" Especially when other countries have opted to use the calendar year.
The answer is rather convoluted and historical:
1155 to 1752: The Tax Year Starts on 25th March
Between 1155 and 1752, New Year’s Day fell on 25th March. The significance being that it was Lady Day, the date of the announcement by the Archangel Gabriel, that Mary was to be the mother of Jesus. Traditionally, 25th March was also when annual contracts between landowners and tenant farmers would begin and end. The rent was also due on this day. So, it made sense to have the tax year in line with this.
1582: all of Europe (except Britain) adopts the Gregorian Calendar
In the 1500's the Julian Calendar was in use. The calendar comprised 11 months of 30 or 31 days, with 28 or 29 days in February.
The problem was, the calendar was out of step with the solar calendar (the actual time taken for the Earth to orbit the sun) by 11.5 minutes a year. This added up to being 10 days out of sync by the late 1500's.
The answer came in the form of a brand-new Gregorian Calendar, which dropped a leap year every century. In 1582, all of Europe elected to adopt the Gregorian Calendar. All except Britain that is, who saw this as another good opportunity to demonstrate its opposition to the Pope Gregory.
1752: Britain adopts the Gregorian Calendar and moves the Tax Year to 5th April
For the next 170 years, Britain held defiantly to the Julian Calendar and ended up 11 days ahead of the rest of Europe.
In 1752 it was decided that Britain should come back into line with Europe. New Year's Day would be 1st January and the extra 11 days would be "lost" by following 2nd September with 14th September.
This sounds simple enough. However, the British people weren't happy that they would be taxed for a full year despite it only lasting just 354 days.
Anxious to ensure that there would be not a loss of tax revenue, the Treasury eventually decreed that the fiscal year should remain as 365 days. This meant that the start of the tax year had to be moved on 11 days from 25th March to 5th April.
1800: The Tax Year moves back a day to 6th April
Since 1800 would have been a leap year under the old Julian Calendar, the Treasury was concerned that it would lose a day of revenue in 1800. To prevent this catastrophe, the tax year was moved to 6th April. Fortunately for us, it was decided to leave it there, for now at least.....