Siddhartha Gautam, the first Buddha, founded Buddhism in the 6th century BCE in Northern India. Two major forms of Buddhism evolved as Buddhism spread across Asia. The Theravada (southern) tradition is found in Burma, Cambodia, India, Laos, Malaysia, Singapore, Sri Lanka, Thailand and parts of Vietnam. The Mahayana (northern) tradition is found in China, India, Japan, Korea, Mongolia, Tibet and Vietnam. Buddhist teachings guide followers to attain liberation from rebirth through Dharma (Four Noble Truths and the Eightfold Noble Path) and Karma (action with cause and effect). Buddhist calendars vary based on the diverse traditions of the adherents’ school of thought. This calendar reflects major dates in all three of the Buddhist calendars.
Anniversary of the Tatsunokuchi Persecution
Nichiren was a Japanese Buddist priest of the Kamakura period (1185-1333), who developed the teachings of Nichiren Buddhism, a branch school of Narayana Buddhism. This day commorates Nichiren's trimuph over his persecution at Tatsunokuchi for his outspoken criticism of other Buddhist doctrines.
Asalha Puja Day (Dharma Day)
This day commemorates the Buddha's first discourse, given to the five monks at Deer Park at Samath, near Varanasi. The day is observed by donating offerings to temples and listening to sermons.
Awakening Day/Bodhi Day
This is the anniversary of the historical Buddha's awakening.
Birth Date of H.H. Dalai Lama Tenzin Gyatso
On this day in 1935, the fourteenth and current Dalai Lama was born.
Birth Date of H.H. Sakya Trizin
On this day in 1945, the head of the Tibetan Sakya Lineage, H.H. Sakya Trizin, was born.
Bodhidharma Memorial
This is the anniversary of the death of Bodhidharma, the twenty-eighth patriarch in the Zen tradition, who brought the Zen transmission from India into China.  
Buddha's Birth Date
This day is the anniversary of the historical Buddha's birth.
Eihei Dogen Kigen Memorial
This day is the anniversary of the death of Eihei Dogen Kigen, founder of the Sōtō Zen school in Japan.
Festival of Higan-e
This festival begins three days before the Autumn Equinox, and finishes three days after that day, happening for a total of one week. It is a time to honour ancestors and to come together to chant the name of Amida Buddha (nembutsu).
Festival of Ksitigarbha (Jizo) Bodhisattva
This festival honours Kistigarbah (Jizo) Bodhisattva, who is one of the four pinicipal bodhisttvas in East Asian Mahayana Buddhism. 
Honen Shonin Memorial
This day commemorates the anniversary of the death of Honen Shonin, the founder of Jōdo Shū.
During the month after the rainy season retreat, lay people may offer the Kathina-robe as part of the general alms-giving ceremony.
Linji Memorial
This is the anniversary of the death of Linji Yixuan, the founder of the Linji school of Chan Buddhism during the Tang Dynasty in China.
Losar (Tibetan New Year)
Losar is celebrated for fifteen days, with the main celebrations during the first three days.
Lunar New Year/Maitreya Bodhisattva's Birthday
The first day after the new (dark) moon is a religious and cultural festival celebrated by Chinese, Vietnamese and Koreans of Buddhist and other backgrounds in the lunar calendar.
Jamyang Khyentse Chokyi Lodro Anniversary
This day acknowledges the life and work of influential spiritual leader Jamyang Khyentse Chökyi Lodrö (1893–1959). Jamyang Khyentse Chökyi Lodrö was a Tibetan lama and a teacher of many of the major figures in 20th-century Tibetan Buddhism.
Magha (Sangha Day)
This day commemorates the spontaneous gathering of 1,250 enlightened arahants (awakened monks) to whom the Buddha delivered the exhortation on the basis of the discipline (ovada patimokkha). Buddhists celebrate both the ideal of creating a spiritual community, and also the actual spiritual community which they are trying to create.
Mahāyāna New Year
Mahāyāna New Year is celebrated for three days from the first full moon day in January. Regional customs or moon sightings may cause a variation of this date.
Memorial of Shan-tao/Zendo Daishi
This is the anniversary of the death of Shan-tao/Zendo Daishi, a Chinese priest of the Tang era who passed away in 681. He developed the practice of reciting the name of Amida Buddha (nembutsu).
Nichiren Foundation Day
This is the anniversary of the foundation of the Nichiren sect in 1253.
Nichiren Shonin Memorial
This day marks the anniversary of the death of Nichiren Shonin.
Nirvana Day
This is the memorial of the historical Buddha passing away. It is celebrated by some Mahāyāna Buddhist traditions on Feb. 8.
Pavarana marks the end of the three months Rains Retreat for the Ordained.
Poson celebrates the anniversary of the arrival of the Arahant Mahinda, son of King Asoka, who first brought Buddhism to Sri Lanka. Poson is characterized by day-long processions and ceremonies at Mihintale which is now the site of a great Buddhist temple at Ambasthale Dagoba.
Sanghamitta Day
Sanghamitta Day celebrates the anniversary of the arrival of Sanghamitta, daughter of King Asoka, who started the Order of Nuns in Sri Lanka and brought a branch of the Bodhi Tree (which still survives in the ancient capital of Anuradhapura). It occurs on the full moon day of December.
Temple Day (Solar New Year)
Buddhists of all schools attend a special service in the temple on this day in dedication of their faith. 
Theravada New Year
In Theravada countries, the New Year is celebrated for three days from the first full moon day in April. On this day, Buddhists visit temples to offer prayers and worship Lord Buddha. Buildings and homes are cleaned, new clothes are worn, and feasts are prepared. 
Vassa (Rains Retreat)
On this day, monks and nuns begin the three month rainy season retreat. Vassa is the period when heavy rain stops the monks from wandering from place to place and causes them to settle down in a temple to apply themselves more strictly than usual to their religious way of life.
Wesak/Buddha Day
Wesak is celebrated on the full moon in May and is an important Buddhist festival. Buddha’s birthday is the most important day of the year for Buddhists. It commemorates the birth, awakening, and passing away (paranibbana) of the historical Buddha, Siddhartha Gautama.