Thai Buddhist Calendar Date

Type a full Gregorian date and the page gives back the Buddhist Era year, the whole date on the Thai calendar, the same date written in Thai script, the weekday, and the subtraction that takes you back to the Gregorian year. The numbers come from the Intl buddhist calendar that ships with your browser rather than from home-made arithmetic, and every date is built and formatted in UTC, so a reader in Bangkok and a reader in Lisbon see the same day.

The Thai civil calendar, called suriyakhati, keeps the twelve Gregorian months and the Gregorian leap rule: 29 February 2024 is 29 February 2567. Only the year count differs, because it starts from the Buddhist Era, anchored to the year after the parinirvana of the Buddha in the Theravada reckoning, which leaves a flat gap of 543 years. Rama V replaced the lunisolar year with a solar one on 1 April 1889. Vajiravudh made Buddhist Era numbering official in 1912, retiring the Rattanakosin Sok count that ran from the founding of Bangkok in 1782. The year 1940 was cut short, running only from April to December, and 1 January 1941 opened as 2484.

That history leaves a trap. A January to March date before 1941 was written with one number less than the modern rule produces, so the page raises a notice and tells you which number the paperwork of the day carried. Two checks you can repeat: 1 August 2026 is 2569, and 31 December 1899 is 2442. What the page will not do is convert the Thai lunar calendar that sets Visakha Bucha and Makha Bucha on full moons, and it will not take a Buddhist date typed in and hand back a Gregorian one.