Parinirvana Day falls on the fifteenth of February in most East Asian Buddhist communities, the date this rule records, though it notes an eighth of February observance kept in some, commemorating the Buddha's final death and entry into complete nirvana. As with Bodhi Day's relationship to the enlightenment, the date belongs to the Mahayana traditions of China, Korea and Japan, which developed a calendar treating the Buddha's birth, enlightenment and death as three distinct commemorations spread across the year rather than a single combined observance.
The Theravada traditions of Sri Lanka and much of Southeast Asia again take the opposite structural approach, marking birth, enlightenment and death together on the single day of Vesak rather than separating them, so the same underlying event, the Buddha's death, is commemorated on an entirely different day and in an entirely different liturgical shape depending on which branch of Buddhism's calendar a community follows. Within Mahayana practice itself, the observance is generally a solemn rather than festive occasion, marked with readings from texts describing the Buddha's final teachings and death, in deliberate contrast to the more celebratory tone of Bodhi Day earlier in the same East Asian calendar, reflecting the difference in what each commemoration marks even though both rest on the same East Asian tradition of separating the Buddha's life into distinct dated observances.