Buddhist calendar

The Buddhist calendar is a set of lunisolar calendars used in many countries such as Tibet, Cambodia, Laos, Myanmar, Bangladesh, India, Sri Lanka, Thailand, and Vietnam, as well as in Malaysia and Singapore. It is also used by Chinese populations for special events and religious holidays. Although these calendars share similar roots, they have small but important differences, like how they add extra months, what they call the months, and how they count years.

In Thailand, the Buddhist Era is a special way to count years that is used alongside both the traditional Thai lunar calendar and the Thai solar calendar. Most Southeast Asian lunisolar calendars are based on an older form of the Hindu calendar, which follows the sidereal year. Unlike the Indian system, these calendars use something called the Metonic cycle to stay aligned, but this method isn't perfect and causes the calendar to slowly drift out of sync over time.

Today, the traditional Buddhist lunisolar calendar is mostly used for celebrating Theravada Buddhist festivals. In Thailand, the Thai Buddhist Era, which is simply a changed version of the Gregorian calendar, is used as the official way to keep track of dates.

Structure

The Buddhist calendar is used in many countries, including Tibet, Cambodia, Laos, Myanmar, Bangladesh, India, Sri Lanka, Thailand, Vietnam, Malaysia, Singapore, and among Chinese communities for religious and official events. Though they share common roots, these calendars have unique features like month names, numbering, and cycles.

The calendar is based on both the phases of the Moon and the cycles of the Sun. This helps keep lunar months in sync with the solar year. A normal lunar year has 354 days, which is shorter than a solar year of about 365.25 days. To fix this difference, extra months and days are added in certain years. This keeps both parts of the calendar aligned. The new year usually starts around April when the Sun enters the sign of Aries, though the exact date has changed over time. Some countries, like Thailand and Cambodia, no longer use the traditional lunisolar calendar to mark New Year's Day.

See also: Burmese calendar § Structure

Sri Lankan Theravada tradition starts Buddha Varsa on 16 Apri 545 BCE. In all Theravada traditions, the calendar's epoch was the day in which the Buddha attained parinibbāna. However, not all traditions agree on when it actually took place. In Burmese Buddhist tradition, it was 13 May 544 BCE. In Thai Buddhist tradition, it was 11 March 544 BCE (–543). As of 2026, the Buddhist new year begins on 21 May 2026 everywhere except Thailand and Tibet. It begins on 1 January 2026 in Thailand and on 18 February 2026 in Tibet (when the new year will become 2153).

The calendar recognizes two types of months: synodic month and sidereal month. The Synodic months are used to compose the years while the 27 lunar sidereal days (Sanskrit: nakshatra), alongside the 12 signs of the zodiac, are used for astrological calculations.

As the Synodic lunar month is approximately 29.5 days, the calendar uses alternating months of 29 and 30 days.

The Buddhist calendar is a lunisolar calendar in which the months are based on lunar months and years are based on solar years. One of its primary objectives is to synchronize the lunar part with the solar part. The lunar months, normally twelve of them, consist alternately of 29 days and 30 days, such that a normal lunar year will contain 354 days, as opposed to the solar year of ~365.25 days. Therefore, some form of addition to the lunar year (of intercalation) is necessary.

The Cambodian, Lao and Thai systems give animal names to the years from a cycle of 12.

The Cambodian calendar also maintains a 10-year naming cycle (numbered one to ten). Cambodians use multiple systems to identify a given year. For instance, 2017 is identified as 2561 Buddhist Era, the year of Rooster, Nuppasak (Year 9). The Thai lunar calendar also uses a similar numbered 10-year cycle.

Accuracy

See also: Burmese calendar § Accuracy

The Buddhist calendars used in Southeast Asia follow lunar months but also try to match the solar year. They add extra months and days to stay close to the solar year. However, these calendars are based on a type of year called a sidereal year, which is a little longer than the actual solar year. Because of this, the calendars slowly move away from the real seasons. They shift about one day every 60 years and four months.

Because of this shift, the New Year's Day, which used to be on March 22, now falls on April 17. There is no big international plan to stop this shift. Thailand has changed its "Buddhist Era" to match the Gregorian calendar, called the Thai solar calendar. In Myanmar, calendar experts try to fix the problem by changing when they add extra months, but this makes it hard to plan calendars far into the future.

History

The Buddhist Era started in Southeast Asia when Buddhism arrived in the early centuries CE. It wasn't a new calendar but a way to count years using the existing lunisolar calendars. At first, the Saka Era was used, starting around 80 CE. Later, the Burmese Era took its place, beginning in Myanmar in 640 CE and spreading to other areas over time.

In Thailand, the Buddhist Era changed in 1912 when King Vajiravudh decided it would follow the Thai solar calendar, starting on April 1. In 1940, it was adjusted again so that the year would start on January 1, making some years shorter. Today, the Thai Buddhist Era is 543 years ahead of the Common Era.

Current usage

The lunisolar calendar helps mark important Buddhist holidays. Many of these holidays are also celebrated as public holidays in many places.

Computer support

The Thai-style Buddhist calendar, which adds the Buddhist era to the Gregorian calendar, is supported in Java 8, iOS, and macOS. These systems can handle dates using this special calendar.