Thailand uses two calendar systems side by side: the solar calendar, which is similar to the Gregorian calendar used globally, and the lunar (lunisolar) calendar, which governs traditional and religious events. Both systems are underpinned by the Buddhist Era (B.E.), which is 543 years ahead of the Gregorian Anno Domini (A.D.). For example, A.D. 2025 corresponds to B.E. 2568.
The Solar Calendar
The Thai solar calendar (สุริยคติ) is Thailand’s official civil calendar. King Chulalongkorn introduced it in 1888 as a local adaptation of the Gregorian calendar】. Initially, the Thai year still began on 1 April, matching the start of the Southeast Asian agricultural year. In 1941, the government moved the official New Year to 1 January to align with international practice and to simplify trade and diplomacy. Months, weeks and days match the Gregorian system, but years are counted in the Buddhist Era (e.g., A.D. 2025 = B.E. 2568).
The Lunar Calendar
Alongside the solar calendar, Thailand observes a lunisolar Buddhist calendar used for festivals, monk ordinations and astrological events. This system divides the year into 12 or 13 lunar months, each beginning with a new moon; occasional leap months align the lunar cycle with the solar year. Important celebrations—such as Visakha Bucha (Buddha’s birthday) and Loy Krathong—are scheduled using lunar months and phases. The Thai lunar date is still printed in newspapers and recorded on birth certificates.
Why Maintain Two Systems?
Historically, the lunar calendar dominated daily life in Siam. Farmers and monks used lunar phases to determine sowing and religious observances. When the solar calendar was adopted for administration and commerce, the lunar calendar continued to guide spiritual life. Today, both systems coexist: government offices, schools and businesses follow the solar calendar, while temples and families consult the lunar calendar for rites of passage and holidays.
Understanding the distinction between Thailand’s solar and lunar calendars helps explain why documents often display two dates and why major festivals seem to float in the Western calendar. It also highlights how Thailand bridges its ancient heritage with modern global conventions.