Mongolian calendar

The traditional Mongol calendar (Mongolian: цаглабар, Tsaglabar or цаг тооны бичиг, Tsag toony bichig) is a lunisolar calendar based on Tegus Buyantu zurkhai system developed in 1747 by monk Ishbaljir (Сүмбэ хамбо Ишбалжир, Sümbe khambo Ishbaljir; 1704–1788). The Mongol 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.

The Mongol new year celebration is Tsagaan sar which is celebrated two months after the first new moon following the winter solstice.

In modern Mongolia, the Gregorian calendar is used, with the traditional calendar only used for traditional celebrations and events based on it.

The European system of chronology is called Аргын тоолол (Argyn Toolol, chronology of method) and the Mongol system of chronology is called Билгийн тоолол (Bilgiin Toolol, chronology of wisdom).

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 Hagas sain ödör (translation: half-good day), and Sunday is referred to as Büten sain ödör (translation: 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.

...
Wikipedia