Blue Monday (date) – Wikipedia

Blue Monday (date) Blue Monday is the name given to a day in January (typically the third Monday of the month) said by a UK travel company, Sky Travel, to be the most depressing day of the year. The concept was first published in a 2005 press release from the company, which claimed to have calculated the date using an “equation”.

https://en.m.wikipedia.org/wiki/Blue_Monday_(date)