In Western superstition, what date is traditionally considered especially unlucky?

In Western superstition, Friday the 13th is traditionally considered especially unlucky. The belief combines two older traditions: Friday’s association with misfortune in some Christian cultures and the number 13’s reputation as an irregular, unlucky number.

The modern fear is often called triskaidekaphobia when it concerns 13, while fear specifically associated with Friday the 13th is sometimes called paraskevidekatriaphobia. Hotels, buildings, and airlines have sometimes omitted the number 13 from rooms, floors, or seating, although this is a commercial response rather than proof that the date causes bad events.

The superstition has no scientifically established causal effect. Its popularity was strongly reinforced by newspapers, novels, films, and popular culture, especially from the late 19th and 20th centuries. The date can occur once to three times in a calendar year, depending on the calendar’s arrangement.