Nirvana Day is a Mahayana Buddhist holiday celebrated in East Asia. By some it is celebrated on 8 February, but by most on the 15 February. In Bhutan, it is celebrated on the fifteenth day of the fourth month of the Bhutanese calendar. It celebrates the day when the Buddha is said to have achieved Parinirvana, or complete Nirvana, upon the death of his physical body.
Passages from the recitations of Nibbana Sutta (Hinayana.) and Nirvana Sutra (mahayana.) describing the Buddha’s last days of life are often read on Parinirvana Day. Other observances include meditation and visits to Buddhist temples and monasteries. Also, the day is a time to think about one’s own future death and on the deaths of loved ones. This thought process reflects the Buddhist teachings on impermanence.
Some Western Buddhist groups also celebrate Parinirvana Day.

How to celebrated
Buddhists may celebrate Nirvana Day by meditating or by going to Buddhist temples or monasteries.
In monasteries, Nirvana Day is treated as a social occasion. Food is prepared and some people bring presents such as money, household goods or clothes.
On Nirvana Day, Buddhists think about their lives and how they can gain the perfect peace of Nirvana. They remember friends or relations who have recently died. They reflect on the fact that death is a part of life for everyone.
The idea that nothing stays the same is important to Buddhism. Buddhists believe that loss and change are things to be accepted rather than causes of sadness.