Currently, it runs at around six or seven, and that must be very confusing for children left to lament that they only get one.
There is however a uniformity to this strange state of affairs in that each of her birthdays falls on the same day of the week year after year ... although the actual date is subject to change.
Her Majesty Queen Elizabeth II was born on April 21, which would have suited everyone just splendidly because it fell on a Monday - meaning the long weekend holiday celebration of her big day could be carried out.
But of course in some years April 21 could be a Tuesday or a Thursday - or at worst a Sunday which is a holiday anyway.
So the Commonwealth nations decree what they decide is the Queen's Birthday and for us it's the first Monday in June.
In Australia it is the second Monday in June while in Canada (and it starts to get a little complicated here) it is the last Monday before May 25, which this year would have been the 19th.
In the UK, the home of the grand lady, it is either the second or third Monday in June - just depends what works best. Over in Fiji it used to be June 12 until Commodore Frank Bainamarama abolished it altogether in 2012 - spoilsport.
On Norfolk Island it is the Monday after the second Saturday in June while on little St Helena (you'll have to look it up in the atlas) they come quite close to the real thing by staging it on the third Monday in April.
Of course it is all about creating that long weekend of celebration, which is very kind of Her Majesty, who must be delighted knowing she could do a bit of a whirlwind trip around the empire and celebrate at least four darn good knees-ups.
