Buddhism gained acceptance into different countries and cultures by changing itself to fit into those cultures. While Buddhism is recognizably Buddhism across all countries in which it is observed, it has made different accomodations to fit into each one. These differences are quite apparent in the area of calendar and religious festivals. On the one hand, Buddhism has no single calendar; it uses the calendars of each country in which it appears. Traditionally, many of the calendars were quite similar, although each country has made different adjustments to accomodate Western systems of time-keeping. On the other hand, religious festivals also vary from country to country. Some holidays are celebrated only in one country, while other may be celebrated in all countries, but at different times.
Before the modern era, most forms of Buddhism were in countries that used a lunar calendar. In Theravada Thailand, for instance, the lunar cycle provides the base for a twelve-month year. Since the lunar year and the solar year do not match in length, there is an elaborate scheme to keep the cycle of lunar months even with the solar year: an additional month is intercalated every two to three years, as well as an extra day or two.
Most Buddhist calendars begin with the Buddha's death (or rather, his entrance into Nirvana), so that according to the Thai calendar, year one (Buddhist Era=B.E.) is 543 bce. Or, in other words, January 1997 ce is in the year 2540 B.E. In Thailand, the New Year was traditionally celebrated the day after Visakha Puja (Buddha Day, a.k.a Wesak), in the middle of the first month, Visakha. Today, Thailand has brought its calendar more in line with the Western (Gregorian) calendar and celebrates New Year on January 1.
For more information on Buddhist holy days, go here. For a list of holy days of many religions, go here.
For the laity, daily worship usually takes place at a shrine in the home. This shrine usually consists of an image of the Buddha and a vase for flowers. The ceremonies usually include puja (usually the offering of flowers), the lighting of candles, the recitation of the Three Refuges and the Five, and specific requests, such as a long life, a good rebirth, and so on. Similar rites will take place in the local chapel and temple.
For the monks, daily worship activities will vary from school to school. They may include meditation, the saying of mantras, reading from sacred texts, and so on.
Monthly worship is regulated by the moon. Four times a month--on the new moon, the full moon, and the days in the middle--lay people may gather at a monastery to learn, worship, and to observe a stricter regimum of life. This latter activity usually means that they will follow the first eight of the Ten Precepts for the day, instead of the five usually expected of the laity. While the laity are not required to do this, they gain merit if they do. This practice of gathering on Moon days is particularly important for Theravada Buddhism.
Twice a month--the new moon and the full moon--the monks will gather for the reading of the pratimoksha, that is, the rules for the moral and religious behavior of members of the sangha. This is required of all healthy monks, and it is a time for examining one's deeds to see if they have been accordance with expectations. If a monk has violated any of the rules, they need to confess it to their fellow monks. This is a private practice for the sangha only; lay persons are not permitted to attend.
There are few religious festivals in Buddhism that are observed by all buddhists at the same time. This is due partially to the nature of Buddhism's historical development and partially to the impact of the regions and countries Buddhism entered. On the one hand, because of the differences in the structure of belief among Theravada, Mahayana and Vajrayana, and among the different schools of Mahayana, there is no one event or person who is understood in the same manner, and thus worshipped in the same manner. So although all forms of Buddhism celebrate the Buddha's life, they do so at different times. Some Mahayana schools celebrate a holiday for their central texts; thus Nicheren celebrates its key work, the Lotus Sutra. Other buddhists celebrate particular bodhisattvas, such as Kuan Yin, and their gifts. Of course, all monasteries have a day celebrating their founding. On the other hand, different countries have celebrations commemorating when Buddhism entered their country. Or, they may celebrate the reign of a particular dynasty. Or, when Buddhism entered the country, it may have taken over a festival from the indigenous religion. So, with all these different reasons for establishing a religious holiday, it becomes clear why so few holidays are celebrated throughout Buddhism. The following discussion will mention just a few holidays, organized by the three divisions of Buddhism.
The main festivals of Theravada Buddhism are Buddha Day and observances linked to the Rain Retreat of the monsoon season. Buddha Day, often called Visakha Puja because it occurs on the full-moon day of the month of Visakha (April-May). It celebrates the Buddha's birth, his attainment of enlightenment, and his death, which Theravadans believe miraculously occured on the same day. The lay people gather at a monastery to hear the telling of the story of the Buddha's life, wash the sacred Buddha images, observe the Five Precepts, and circumnambulate the reliquary.
With regard to the rainy season retreat, which the monks observe from July to October, Theravada has a small celebration at the beginning of the rains when the monks traditionally enter retreat. This is called Magha Puja, because it occurs on the full-moon of the month of Magha. It consists primarily of circumnambulating the reliquary and listening to sermons on the monastic order. In countries where it is customary for young men temporarily to enter the sangha as their rite of passage into adulthood, it usually happens on this day. The Rain Retreat usually ends with the Kathina ceremony, where the laity give the monks robes and other needed items, and the monks read certain sutras for the benefit of the deceased.
In Thailand, a Theravadan country, Chakri Day in April commemorates the founding of the current dynasty. Many acts of worship are woven into the day's observances; indeed, the famous Emerald Buddha statue of Bangkok plays a key role in the ceremonies, receiving homage from the Emperor.
In Mahayana Buddhism, the important action of Buddha's Day is the washing of the Buddha's images. Celebrated in China, Korea and Japan on the eighth day of the fourth lunar month, the main focus of this celebration from the sangha's perspective is the Buddha's attainment of enlightenment. The laity, however, see it more involved with attaining material blessings (although it is not as commercial as Christmas).
Mahayana Buddhism, especially in China, celebrates the life of the bodhisattva Kuan Yin: her birthday on the nineteenth day of the second lunar month, her enlightenment on the nineteenth of the sixth month, and her entry into nirvana on the nineteenth of the ninth month.
All Souls' Feast in China constitutes an adoption by Buddhism of an earlier celebration. This holiday comes from China's veneration of ancestors and is thought to help ease the lot of ancestors of the preceding seven generations.
In Vajrayana Buddhism, the Buddha's life is celebrated on four different days: his conception is observed on the fifteenth of the first lunar month, his attainment of enlightenment on the eighth day and his death on the fifteenth day of the fourth month, and his birth on the fourth day of the sixth month.