The Mongolian calendar may refer to a number of different lunisolar calendars related to the Chinese and Tibetan calendars.^[1] These calendars (Mongolian: цаглабар, romanized: tsaglabar or цаг тооны бичиг, tsag toony bichig) have largely been replaced in day-to-day use with the Gregorian calendar (Аргын тоолол, Argyn toolol, 'chronology of method'), however the traditional calendar (Билгийн тоолол, Bilgiin toolol, 'chronology of wisdom') is still used for a variety of traditions such as the date of festivals like Tsagaan Sar (the Mongolian new year), horoscopy, and zodiac signs.

The traditional calendar as used in Mongolia today is a lunisolar calendar based on Tegus Buyantu zurkhai^[2] system developed in 1747 by monk Ishbaljir (Сүмбэ хамбо Ишбалжир, Sümbe khambo Ishbaljir; 1704–1788). The year is composed of either 12 or 13 lunar months, each beginning and ending with a new moon. A thirteenth month is added every two or three years, so that an average year is equal to the solar year.^[3]

The Mongol traditional new year celebration is Tsagaan Sar which is celebrated at the second new moon following the winter solstice.

The twelve months of the year are referred to by their number, such as first month, second month, and so on.

In colloquial usage, the first 5 days of the week are referred to as first day, second day, etc. Saturday is referred to as Хагас сайн өдөр (Khagas sain ödör, "half-good day"), and Sunday is referred to as Бүтэн сайн өдөр (Büten sain ödör, "full good day"); a result of 5 full working days and Saturday as a half working day during the communist era.

The names of Tibetan origin are used in more formal settings, and almost exclusively in written documents, while the Sanskrit names are practically absent in modern usage.

• Public holidays in Mongolia