Add bad winter weather and debt together. Multiply that by the amount of time since Christmas to the power of the amount of time since failing your new year's resolutions. Then divide that by the sum of low motivational levels and the urge to take action.

What do you get?

If you ask Cliff Arnall, a former lecturer at Cardiff University, he'll say "Blue Monday," the most depressing day of the year.

But ask Dean Burnett, a neuroscientist and current Cardiff lecturer, and he'll say it's a PR stunt based on pseudoscience.

The idea of Blue Monday dates back to a 2005 campaign by Sky Travel. The company wanted to encourage people to take January vacations, so they reached out to Arnall, who developed his equation to find the most depressing day of the year.

Media, the public, and even other companies latched onto the idea. A U.K. group started a website dedicated to "beating Blue Monday." Another group,, encourages acts of kindness on the date.

Scientists, however, say there is no evidence that Blue Monday causes any more sadness than other specific days of the year. Burnett has been outspoken on the topic, publishing multiple blogs in The Guardian dedicated to dispelling the myth.

"This claim is incorrect. It is unscientific. It is pseudoscientific. It is uber-pseudoscientific," he wrote in 2013.

And yet, Blue Monday persists.

Burnett blames slow January news cycles, general post-holidays discontent, and "confirmation bias" for the term's endurance.

"(People) feel down at this time of year, and the Blue Monday claim makes it seem like there are scientific reasons for this," Burnett said in an email exchange. "It also breaks down a very complex issue into something easily quantifiable and simple, and that tends to please a lot of people, giving the impression that the world is predictable and measurable."

Though a particular day may not be "the most" depressing, the Canadian Mental Health Association does recognize that people tend to be affected by Seasonal Affective Disorder at this time of year.

The disorder, the association says, can range from mild winter blues to a serious condition that can interfere with daily life. And contrary to popular belief, it does not only strike in winter. Though less common, some people also suffer from summer depression.

"(Seasonal affective disorder) can be a debilitating condition, preventing sufferers from functioning normally. It may affect their personal and professional lives, and seriously limit their potential," the association's website says.

Burnett says he objects so strongly to Blue Monday because of how it leads to misunderstandings about clinical depression and genuine mental illness.

"It gives a wildly misleading portrayal of how mood and mental states work, suggesting they can be quantifies with a simple (although nonsensical) equation," he said.