After the creation of their realm at the beginning of the Second Age, the Dúnedain of Númenor devised a calendar, largely based upon the Calendar of Imladris used by the Elves. By the latter part of the Third Age, a modified version of this calendar had been adopted by almost all folk using Westron (Common Speech).
The Elves of Middle-earth had devised the first forms of calendars, which were based primarily upon observed cycles of growth; their divisions of time were chosen more for ritual, rather than practical, reasons. It was because of this system, in which one Elven year was equivalent to 144 mortal years, that the early Númenoreans developed a calendar which fit their own needs.
They adopted the Eldarin cycle of 365 days – known as the loa, or ‘growth’ – and retained the Mannish custom of beginning this cycle at Yule (compared to the Elves, for whom the new cycle began mid-spring). They also abandoned two of the six Elvish seasons – ‘fading’ and ‘stirring’ – and recognised instead just spring, summer, autumn, and winter. (Unlike the Elven seasons, these were unfixed in length and simply indicated a change in temperature, length of day, or vegetation.)
To better simplify their 365-day calendar year, the Dúnedain divided their loa into twelve months (astar) of nearly equal length (ten months had 30 days; two had 31). Additionally, there were five Eldarin days which belonged to no season specifically; these were reduced to three and then redistributed across the calendar. Another day – Eärenya, ‘Sea-Day’ – was added to produce a seven-day week, and the Dúnedain now began to recognise the day as beginning at sunrise and ending at sunset, rather than from sunset to sunset as the Elves did.
Quenya was the language most commonly used for the names of the months, though the Dúnedain often used their Sindarin forms, and Hobbits typically used Mannish ones.
The calendar for one loa was:
(Q) Yestarë, (S) Minien – first day
(Q) Narvinyë, (S) Narwain, [ January] – “New Sun,” 30 days
(Q) Nénimë, (S) Nínui, [February] – “Watery,” 30 days
(Q) Súlìmë, (S) Gwaeron, [March] – “Windy,” 30 days
(Q) Víressë, (S) Gwirith, [April] – “New/young/budding,” 30 days
(Q) Lótessë, (S) Lothron, [May] – “Flower month,” 30 days
(Q) Náríë, (S) Nórui, [June] – “Sunny,” 31 days
Loëndë – Midsummer’s Day (replaced by two Enderi – middle days – during a leap year, which occurred every fourth year; excluding the last year of a century)
(Q) Cermië, (S) Cerveth, [July] – “Cutting,” 31 days
(Q) Urimë, (S) Urui, [August] – “Hot,” 30 days
(Q) Yavannië, (S) Ivanneth, [September] – “Fruit-giving,” 30 days
(Q) Narquelië, (S) Narbelet, [October] – “Sun-fading,” 30 days
(Q) Hísimë, (S) Hithui, [November] – “Misty,” 30 days
(Q) Ringarë, (S) Girithron, [December] – “Cold/shivering month,” 30 days
(Q) Mettarë, (S) Penninor – last day
The days of the week, in their Quenya/Sindarin/Mannish forms, are:
(Q) Elenya, (S) Orgilion – Starday
(Q) Anarya, (S) Oranor – Sunday
(Q) Isilya, (S) Orithil – Moonday
(Q) Aldëa, (S) Orgaladh – Treeday
(Q) Menelya, (S) Ormenel – Heavenday
(Q) Valanya or Tárion, (S) Orbelain or Rodyn) – Valarday
(Q) Eärenya, (S) Oraearon – Seaday
Those Númenoreans who survived the Downfall brought their Calendar back to Middle-earth with them. For the first two thousand years, the Kings’ Reckoning was left unchanged; but after the passing of Gondor’s last King, the Steward Mardil introduced a revised Calendar (TA 2060), known as the Stewards’ Reckoning. (In reality, this new Calendar was just the Númenorean system with its accumulated deficits of 5500 years re-adjusted.) In this form, the Calendar was adopted by most of the other Westron-speaking peoples of Middle-earth. The Hobbits, however, preserved the original Kings’ Reckoning, which they had used in the Shire prior to the fall of the North-kingdom, modifying it only slightly for their own use.