The term Mongolian calendar (Mongolian: цаглабар, romanized: tsaglabar or цаг тооны бичиг, tsag toony bichig) refers to a number of different calendars, the oldest of which was a solar calendar.^[1] The beginning of the year was autumn. The year was divided into 4 seasons. The seasons begin at the equinoxes and the solstices of the sun. This calculation was changed in 1211, and the new year was celebrated in the spring. Spring began on March 22.

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In 1282, Kublai Khan revised the Chinese calendar and began to include his homeland Mongolia in this calendar.

The traditional Mongol calendar 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 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 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. In 2022, the second new moon was on 1 February in Mongolia. ^{[citation needed]}

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

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).

• Public holidays in Mongolia