Cliff Arnall, a health psychologist at the University of Cardiff, specialising in confidence-building and stress management, said the prediction was the result of some gruelling mathematics.
Post-Christmas blues, the return to work after the holidays, mounting bills to pay for the parties, the challenge of keeping New Year's resolutions, the slender prospects of fun in the weeks ahead and chilly winter temperatures for those in the northern hemisphere all add up, he said.
These factors, which he combined in a complex mathematical formula, revealed that the Monday closest to January 24 would be the most dismal day of the year.
So now we know, would we not have been better off without the bad news? Not at all, according to Arnall.
Those in the know are in a better position to beat the blues, he insisted.
"You can us it as a springboard to make changes. It can encourage people," he said.
However, those in misery on Monday at least have something to look forward to.
According to the same mathematical formula, June 23 is the happiest day of the year.