Stressed worker
Back to work blues and post-Christmas debt are allegedly contributing factors to Blue MondayReuters

It is supposed to be the most depressing day of the year today, due to an unfortunate combination of post-festive debt, the failure of new year's resolutions and the time passed since Christmas.

For most, January is a time of expanded waistbands and tightened purse strings, which when combined with the first day back at work, makes the month understandably miserable. But why does Blue Monday allegedly fall on the third Monday of January?

The concept was started as a publicity campaign by travel agents Sky Travel to sell a last-minute getaway. The theory was first published in 2005 a press released under the name of Cliff Arnall, who at the time was a tutor at the Centre for Lifelong Learning – a Further Education centre associated with Cardiff University.

Later, however, the Guardian printed a statement from the university distancing itself from the psychology professor: "Cardiff University asked us to point out that Cliff Arnall... was a former part-time tutor at the university but left in February."

blue monday
The alleged formula for Blue MondayWiki Commons

Debunked countless times by scientists and psychologists, Blue Monday is largely considered pseudoscience and a term created for PR purposes only.

But, according to Arnall, the date can be calculated using several factors.

Debt level, pay time since Christmas, the abandon of new year's resolutions, low motivation levels and cold weather are all to blame for the most depressing day of the year.

According to a press release by a mental health charity, there is a formula to calculate Blue Monday – although units of measurement are not defined. It is broken down as follows: W = weather, D = debt, d = monthly salary, M = low motivational levels, Na = the feeling of a need to take action.

Most are unconvinced there is one specific day for misery, though. Journalist Michael Marshall wrote in the Guardian in 2014: "Keener observers have spotted that today isn't actually the most depressing day of the year at all, but merely the day a particular travel company wanted to nudge you into booking a winter blues-alleviating holiday, hiring a media-friendly scientist-type along the way to add a veil of legitimacy to their advert."

British physician, academic and scientific writer Ben Goldacre suggested in 2011 that Blue Monday could lead to serious issues concerning the perception of mental health: "It's also worth thinking about the wider consequences when we indulge, deploy, and therefore normalise, nonsense... This does not feel like a constructive contribution to stigma, or the perception of serious mental illnesses."