Today has been deemed "Blue Monday," the most depressing day of the year.

People start to deal with post-Christmas bills coming in, cold temperatures, and shorter days.

Psychologist Cliff Arnall took all that into account when he came up with a formula to show the third Monday in January is the most depressing day of the year.

The formula is weather plus debt minus salary multiplied by the time since Christmas to the time since failure to fulfill New Year's resolutions.

Then take that and divide by motivational level and the need to take action.

This is also the time of year where there are many cases of SAD, or Seasonal Affective Disorder, when people experience symptoms of depression during the winter.

The Canadian Mental health Association estimates 2% and 3% of the general population may have SAD. Another 15% have a less severe experience described as the "winter blues."

Basically a lack of sunlight causes depression symptoms, experts say.

Research sponsored by an ice cream company has deemed June 17 to be the happiest day of the year.