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.