Gregorian months and days, counted in the Buddhist Era.
Thailand's civil calendar uses Gregorian months and days with Buddhist Era year numbering, 543 years ahead of the Common Era. A Thai government document dated 1 January 2570 and one dated 1 January 2027 are the same day.
Because the day and month are familiar, the year is the only thing that signals which calendar is in play — and a four-digit year that looks like a typo is easy to correct in the wrong direction.
The calendar was aligned to the Gregorian in 1941, when the Thai year was also moved to begin in January. Dates before that require care that dates after it do not.
The Buddhist Era is the year count. The Thai solar calendar is the civil calendar that uses it, on an otherwise Gregorian structure.
See also buddhist era · gregorian calendar · epoch
We hold this as not stored — Thai observances are published as Gregorian dates. See what we hold.