Why is Friday the 13th unlucky?
No single source explains it. The usual strands are thirteen at the Last Supper, Friday as the day of the crucifixion, and a later fear that merged them. The widely told story about the Knights Templar is popular and has weak support.
Last reviewed October 20, 2026
What each tradition says
The eastern Mediterranean, first century CE, and many branches since
Christian tradition
Thirteen people were at the Last Supper, with Judas often counted as the thirteenth, and Good Friday is the day of the crucifixion. Each has been offered as a root for the unease, and the two together make a tidy story. A named Friday the 13th as a source of dread is easier to find in the early twentieth century than much earlier.
Scandinavia, recorded in Iceland in the thirteenth century
Norse mythology
A story often retold says Loki arrived uninvited as the thirteenth guest at a gods' feast. It is told more as a parallel than as a source, and the thirteenth guest framing is a retelling and not something the old texts state in so many words.
Found everywhere, in every era, with no single point of origin
Folk omen custom
Fear of the number thirteen has a clinical name, triskaidekaphobia, which was in use by 1910. Many buildings still skip a thirteenth floor. The arrest of the Knights Templar on Friday 13 October 1307 is often credited as the origin, and there is no good evidence that anyone linked the date to the superstition until much later.
How to weigh it
Because several explanations overlap, none of them can be confirmed on its own, and that is typical of a superstition that grew by retelling. Some people really do feel uneasy on the date, and the unease is real even when the origin story is not. Plan the day as you would any other.