Vesak is an annual holiday observed traditionally by practicing Buddhists in all countries. The exact date of Vesak varies according to the various lunar calendars used in different traditions.

In Theravada countries following the Buddhist calendar, it falls on the full moon Uposatha day (typically the 5th or 6th lunar month). In China it is the fourth month in the Chinese lunar calendar, coinciding with the first full moon of that month. The date varies from year to year in the Western Gregorian calendar but falls in April or May. Sometimes informally called "Buddha's birthday," it actually encompasses the birth, enlightenment Nirvana, and passing (Parinirvana) of Gautama Buddha.