One Awakening, Kept on Two Different Calendars

Bodhi Day falls on the eighth of December in the East Asian Buddhist calendar, the date this rule records, commemorating the Buddha's enlightenment beneath the Bodhi tree at Bodh Gaya. The date belongs specifically to the Mahayana traditions of China, Korea and Japan, where it developed within a monastic calendar that keeps the Buddha's birth, enlightenment and death as three separate commemorations across the year. In Japanese Zen practice the day is called Rohatsu, and it is prepared for by an intensive week long meditation retreat, a sesshin, that concludes at dawn on the eighth, echoing the tradition that the Buddha himself sat in unbroken meditation through the preceding night before his awakening.

Theravada Buddhism, the tradition dominant in Sri Lanka and much of Southeast Asia, does not mark a separate Bodhi Day at all. It instead commemorates the birth, enlightenment and death of the Buddha together on a single day, Vesak, reckoned by the lunar calendar and falling in the month of Vaisakha, typically in April or May. The difference is not a disagreement about when the enlightenment happened but a difference in liturgical structure, whether the tradition's calendar treats the three events as one commemoration or three, and the December date this rule records belongs entirely to the East Asian branch that chose to separate them.