If you find yourself whistling the tune of 'Oh happy day' with an extra spring in your step there may be a mathematical formula to explain your unexpected good humour.
According to Welsh psychologist Dr. Cliff Arnall, Friday June 23 is the happiest day of the year.
The seasonal disorders specialist has devised a formula that measures good mood through outdoor activity, high energy levels and more sunlight.
The equation Arnall devised to find the happiest day is O + (N x S) + Cpm/T + He.
O stands for being outdoors and outdoor activity, N for nature, S for social interaction, Cpm for childhood summers and positive memories, T for temperature and He for holidays and looking forward to time off.
Today was also pinpointed as the happiest day of the year because of its added "thank goodness it's Friday" feeling.
"Happiness is associated with many things in life and can be triggered by a variety of events," said Arnall, who works part-time as a teacher at Cardiff University.
"Whether it's a sunny day, a childhood memory, or something as effortless as eating a delicious ice cream - I wanted my formula to prove the key to happiness can really be that simple," said Arnall.
Arnall's mention of ice cream was not coincidental.
The research, sponsored by the British ice cream maker Wall's, was commissioned to coincide with the opening of a photographic competition asking people to capture moments of happiness associated with the summer.
A spokesman for Wall's said: "The formula follows research recently revealed by Wall's Ice Cream showing ice cream actually makes you happy because it lights up the brain's pleasure zones."
Arnall dismissed suggestions that rainy weather in various parts of the world could render his equation null and void.
"The issue about the weather specific to this formula is the temperature, which is still reasonably high," he told the British Broadcasting Corp.
"This will pass - you do get summer storms and skin is waterproof.
It was Arnall who used a similar method to conclude January 23, or Canada's last election day, was the most depressing day of the year.
That study was commissioned by Sky Travel, which Arnall remembered well when he released his findings. "A holiday could be just the solution to cheer everyone up," he said at the time.
