Tax balance dates around the world are often quite straight forward. Most incorporate a full calendar month, like the standard New Zealand balance date of 31 March. However the standard balance date in the UK is the 5th of April – and there’s quite a story behind this.
The British Empire followed the Julian type calendar until 1752 when they changed to the new standard Gregorian. The Julian calendar was slightly different than the Gregorian; longer by about 11.5 minutes each year. The Gregorian calendar was introduced to Europe by Pope Gregory XIII in 1582, and had taken over as the standard throughout most of Europe. The 11.5 minute difference slowly added up resulting in the British Empire being 11 days behind the rest of Europe.
To make sure the British Treasury didn’t lose out on any revenue, they added this 11 day difference onto their existing tax balance date of 25th March (New Year’s Day in the 18th century). These additional days gave a new balance date of April 4th.
Later in the year 1800, the old Julian calendar was due for a leap year day but the current Gregorian calendar was not. The British Treasury made sure to account for this by moving the balance date to April 5th, which remains the date used today.