In the fiction of J. R. R. Tolkien, Durin's Day is a rare event noted by Dwarves. The first day of the Dwarves' year is the day that begins the last cycle of the Moon to begin in autumn. When on this day both the Sun and Moon may be seen in the sky together, it is called Durin's Day.

In The Hobbit, the writing on the map that Gandalf had received from Thráin II mentioned Durin's Day. It predicted that on Durin's Day the last light of the Sun as night fell would reveal the secret door into the Lonely Mountain.