Feeling rotten today? Cheer up -- you're probably not the only one. That's because today is "Blue Monday," the most depressing day of the year, they say, and chances are most of us are under the same dark cloud.

"Blue Monday" isn't what you'd call a widely accepted scientific fact; it's an idea coined in 2005 by psychologist Cliff Arnall, a former part-time lecturer at Cardiff University in Wales.

"I was asked a number of years ago if I could come up with what I thought was the most depressing day of the year. And I thought that was a really good challenge and I was curious to see what day that would be," Arnall told CTV's Canada AM from Brecon, Wales on Monday.

Arnall came up with a bit of a convoluted formula to show that the third Monday in January is the most depressing day of the year.

That's the day, he reasoned, when the lousy weather conspires with our holiday bills and our depression over our failed New Year's resolutions to make this day downright awful.

If the cold and cloudy weather weren't enough to make us blue, many of us are realizing today that we really couldn't afford all those things we bought ahead of Christmas. Then, there's those New Year's resolutions we made that have fallen by the wayside or been outright abandoned.

"Motivational levels also tend to be quite low at this time of year," Arnall explained. "You've got something called the ‘hibernation effect,' when people tend to be more lethargic, they eat more than they really need."

Put it all together and you've got the most depressing day of the year.

Or a great marketing gimmick.

The story goes that Arnall created his formula as part of a marketing campaign for a travel company, to give Britons a good reason to book a vacation abroad.

Pseudo-science or not, the idea that we have hit the nadir of winter's most depressing days seems to be an idea that people love to latch onto. Log on to Twitter and you'll likely find that #BlueMonday is a top trend. Open a newspaper or log onto a news website (such as this one) and chances are good you'll find a story on Blue Monday.

Of course, there are those who accuse that pointing out these articles that today is a depressing day will just make it a self-fulfilling prophecy. Perhaps true.

But you've already made it this far in the day. And now you can start looking forward to June 17, the day that Cliff Arnall -- this time, reportedly paid by an ice cream company -- has decided is "the happiest day of the year."

It's only 21 weeks away.