Dedicated BE 2553 (Buddhist calendar)- many Thai celebrations are of a Buddhist nature, they refer to the Buddhist religious calendar, which is dependent on the moon-cycle. Therefore certain celebrations vary within the month from year to year. The Buddhist calendar is 543 years older than the Christian / Gregorian calendar, the year 2000 thus corresponds with the year 2543.
The Buddhist Calendar is calculated differently in various parts of the world. The most common type of Buddhist calendar is lunar and begins roughly in December or January of the Christian / Gregorian calendar. Each month is approximately 29 or 30 days, depending upon the length of the each moon.
In essence the Buddhist calendar is similar to the Hindu calendar but uses a different moon to begin the New Year. Every few years an extra intercalary or leap day is added after the 7th Month; occasionally an extra month is added as well. Because of this system, it is often quite difficult to predict when Buddhist holidays will be celebrated from year to year.