The Calendars is the fourth chapter of The Peoples of Middle-earth, in which Christopher Tolkien discussed the early texts of what would become Appendix D to The Lord of the Rings. Christopher identified two versions of the text which he labeled D1 and D2, and stated that they were written in parallel with the two versions of the Appendix on Languages, F1 and F2. He believed that all four texts (F1, F2, D1, and D2) were written before the summer of 1950 and says that D1 was associated with an envelope postmarked August, 1949.
D1 was a brief, rough manuscript while D2 was a fair copy that was made not long after the composition of D1. However, the two texts differ significantly and so both were included in this chapter.:119
The earlier text, D1, has an Eldarin calendar that is unrelated to the one in the published Appendix D. In D1 the Elves counted off in centuries with years 366 days in length, with subtractions made at regular intervals to bring the calendar into alignment with the astronomical year. The Númenórean system was much closer to the Hobbit calendar in this text than in Appendix D.:124
In D2 the Eldarin system was altered but still does not match the details of Appendix D. The Númenórean system saw greater changes in the transition to D2, but again varies from Appendix D.:131 D2 did see the addition of the revised system under the Stewards that was not adopted by the Hobbits. D2 made no reference to the new calendar introduced after the fall of Barad-dûr while D1 did have a brief note to that effect.:132
The calendar used by Gondor in the Fourth Age is described next, again not in the final form published in Appendix D. Since the beginning of the year was substantially shifted in the new system, Tolkien created a table that clearly showed the correspondence of dates between the new system, the Shire Reckoning, and the Steward's Reckoning.:134
Christopher then stated that the "elegantly balanced structure" of D2 was dropped and replaced by the text of Appendix D.:135 He found no further texts after D2 before the typescript of Appendix D, which he described as "rough and a good deal emended". He believed that his father was still in the process of developing the Calendars when the crush to submit the text became urgent, and had Tolkien been able to finish his ideas Appendix D would have been "markedly different".:136