If you found it hard to get out of bed on Monday and you're feeling grumpy you're not alone - it is officially the most depressing day of the year!
Experts used some complicated maths to work out that Monday 21 January is the day when people are most unhappy.
It's because Christmas is over, the weather is miserable and lots of people have broken their New Year Resolutions.
All this means the time of year makes people more gloomy than they might be at other times.
Top tips to get help you through the day include smiling at everyone you meet and doing some exercise.
And if you've messed up your New Year's resolutions, put it down to a mistake, and then start them again.