Today is 'saddest day of the year' -- and there's a 'Blue Monday' equation that 'explains' why

Wintry weather. Post-holiday debt. Failed New Years resolutions. And everyone back in the office after taking time off.

Those things added together amount to what is believed to be the most depressing day of the year for many: today, January 19, dubbed “Blue Monday.”

The origin of “Blue Monday” dates back to a 2005 campaign by Sky Travel. The company enlisted former Cardiff University lecturer Cliff Arnall to develop an equation to find out what day is the most depressing of the year.

The equation -- shown in the image above -- uses six factors: weather (W), debt (d), time since Christmas (T), time since failing our new year’s resolutions (Q), low motivational levels (M and N).

Scientists have disputed the equation, but how do you feel today?