Lord of the Rings: The Animated Musical | Appendix D: Shire Calendar
While Appendix D is named for the Shire Calendar, this section actually covers calendars from multiple Middle-earth cultures spanning thousands of years. The construction of these calendars presented an unresolved mystery: why were they so similar to modern Western calendars? A real-world explanation was that Tolkien was most familiar with the Gregorian calendar, but a Middle-earth explanation was more complex.