The third Monday of January gets the title thanks to post-Christmas blues, cold dark nights and the arrival of hefty credit card bills.
And businesses could be losing up to £93 billion thanks to “workplace malaise” and low productivity, according to the University of Exeter.
Spark and Mettle, a London charity that supports young people, is encouraging people to get into the kitchen and bake.
Hugh Fearnley-Whittingstall and Prue Leith have donated recipes including a marmalade muffin and a goat’s cheese and onion tartlet to the Flour-ish campaign. The recipes can be accessed at flour-ish.org.uk.
Charity founder Eugenie Teasley said: “One of the simplest ways to lift your spirits is to do something for someone else. By baking and sharing with friends, family or colleagues, you can spread a little cheer and bolster your own mood too.”
But other people took to Twitter to post messages about how great they feel today.
@Beffnay tweeted: “Zumba done and now time to catch up on Sherlock. Who says today is blue Monday?”
@JayCruik was having a great day too, saying: “Blue monday? Forget that, me and @DoddsKathryn are buzzing away haha.”