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Thai B.E. ↔ C.E. converter

B.E. = C.E. + 543 works for most dates, but before 1941 the Thai year began on 1 April, so January–March dates differ by 542. This converter gets every date right.

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Full date

Why +543 alone is wrong for some dates

  • Siam adopted the solar calendar on 1 April 1889 (R.S. 108), with the year beginning on 1 April.
  • The Calendar Year Act B.E. 2483 moved New Year to 1 January from 1941, so B.E. 2483 lasted only nine months: 1 April – 31 December 1940.
  • So 1 January – 31 March of every year before 1941 still belongs to the previous B.E. year: add 542, not 543. 1 Feb 1940 is B.E. 2482.
  • Even JavaScript’s built-in buddhist calendar adds 543 to every date: for 1 Feb 1940 it gives “1 กุมภาพันธ์ 2483”, where the right answer is “วันพฤหัสบดีที่ 1 กุมภาพันธ์ พ.ศ. 2482”.
  • The Rattanakosin Era (R.S.) ran from 1 April R.S. 108 to 31 March R.S. 131, then B.E. 2456 took over. B.E. = R.S. + 2324.

FAQ

What year is 2569 B.E.?

2026 C.E. (B.E. minus 543), which holds for every date of the current year.

How do I convert C.E. to B.E.?

Add 543 from 1 January 1941 on, and for April–December dates before that. For January–March before 1941, add 542.

Why did B.E. 2483 have only nine months?

New Year moved from 1 April to 1 January starting in 2484, so January–March 1941 became the start of 2484 instead of the end of 2483.

What is R.S.?

The Rattanakosin Era, counted from the founding of Bangkok, official 1889–1913. B.E. = R.S. + 2324; C.E. = R.S. + 1781 (+1782 for January–March).

Sources