> The Lord of the Rings
/ The Silmarillion
The calendar of the dwarves is only hinted at in Prof. Tolkien's works, in fact it appears in only this one paragraph:
"Then what is Durin's Day?" asked Elrond.
"The first day of the dwarves' New Year," said Thorin, "is as all should know the first day of the last moon of Autumn on the threshold of Winter. We still call it Durin's Day when the last moon of Autumn and the sun are in the sky together.
But as with all things Tolkien, we can extrapolate a great deal from a few words. The one thing apparent is that the Dwarves had a lunar calendar, instead of a solar like the rest of the races of Middle-Earth and our own Gregorian calendar. To make this work, the calendar must have used the changes and phases of the moon as a central timing point. These phases last about four weeks, which leads to the major problem: twelve lunar months (One lunar year) would only amount to 354 days, leaving 11 unaccounted for. This is a problem because the seasons follow the solar year, and the calendar would lose 6 months a little over every 17 years.
The solution given to this seems to be that the Dwarves just reset their calendar every year. This sentence: "the first day of the last moon of Autumn on the threshold of Winter," tells us they waited for a time when the solar and lunar coincided and started anew with another Durin's Day. Because of this there was no need for a "leap year," because some years would have twelve months and others thirteen.
This is one of the great enigmas of Middle-Earth left by Prof. Tolkien and everything is almost completely speculation. The one thing that is certain, however, is that if Tolkien did create a complete and lunar Dwarven calendar, it would have been a working, usable system and not rubbish imagination.
For you dwarves out there, the next verifiable Durin's Day is October 14, 2004, so comb your beards and prepare your rum now! (There are other dates that could be Durin's Days, but they all depend on where the dwarf is at on the globe.)