The traditional Korean calendar is a lunisolar calendar, like the traditional calendars of other East Asian countries. Dates are calculated from Korea's meridian, and observances and festivals are based in Korean culture.
The Gregorian calendar was officially adopted in 1896, but traditional holidays and age-reckoning for older generations are still based on the old calendar. The biggest festival in Korea today is Seollal, the first day of the traditional Korean New Year. Other important festivals include Daeboreum also refer to as Boreumdaal (the first full moon), Dano (spring festival) and Chuseok (harvest moon festival), and Samjinnal (spring-opening festival). Other minor festivals include Yudu (summer festival), and Chilseok (monsoon festival).
The traditional calendar designated its years via Korean era names from 270 to 963. Then Chinese era name with Korean era names were used few times until 1894. In 1894-1895, The lunar calendar was used with years numbered from the foundation of the Joseon Dynasty in 1392.
The Gregorian calendar was adopted on 1 January 1896, with Korean era name "Geonyang (건양 / 建陽, "adopting solar calendar")."
From 1945 until 1961 in South Korea, Gregorian calendar years were counted from the foundation of Gojoseon in 2333 BC (regarded as year one), the date of the legendary founding of Korea by Dangun, hence these Dangi (단기 / 檀紀) years were 4278 to 4294. This numbering was informally used with the Korean lunar calendar before 1945 but is only occasionally used today and mostly used in North Korea.
- The Korean zodiac of 12 Earthly Branches (animals), which were used for counting hours and years;
- Ten Heavenly Stems, which were combined with the 12 Earthly Branches to form a sixty-year cycle;
- Twenty-four solar terms (jeolgi / 절기 / 節氣) in the year, spaced roughly 15 days apart;
- Lunar months including leap months added every two or three years.
The lunar calendar is used for the observation of traditional festivals, such as Seollal, Chuseok, and Buddha's Birthday. It is also used for jesa memorial services for ancestors and the marking of birthdays by older Koreans.
Traditional holidays 
|Seollal||Lunar New Year's Day||An ancestral service is offered before the grave of the ancestors, New Year's greetings are exchanged with family, relatives and neighbours; bows to elders (sebae), yutnori.||Day 1 of Month 1||sliced rice cake in soup (tteokguk), honey cakes (yakwa).|
|Daeboreum||First full moon||Greeting of the moon (dalmaji), kite-flying, talisman burning to ward evil spirits (aengmagi taeugi), bonfires (daljip taegi)||Day 15 of Month 1||rice boiled with five grains (ogokbap), nut eating (bureom), wine drinking (gwibalgisul)|
|Meoseumnal||Festival for servants||Housecleaning, coming of age ceremony, fishermen's shaman rite (yeongdeunggut)||Day 1 of Month 2||stuffed pine-flavoured rice cakes (songpyeon)|
|Samjinnal||Migrant swallows return||Leg fighting, fortune telling||Day 3 of Month 3||Azalea wine (dugyonju), pancake (dungyeon hwajeon)|
|Hansik||Beginning of farming season||Visit to ancestral grave for offering rite, and cleaning and maintenance.||Day 105 after winter solstice||cold food only: mugwort cake (ssuktteok), mugwort dumplings (ssukdanja), mugwort soup (ssuktang)|
|Chopail||Buddha's birthday||Lotus Lantern festival||Day 8 of Month 4||rice cake (jjinddeok), flower cake (hwajeon)|
|Dano||Spring festival||Washing hair with iris water, ssireum, swinging, giving fans as gifts||Day 5 of Month 5||rice cake with herbs (surichitteok), herring soup (junchiguk)|
|Yudu||Water greeting||Water greeting, washing hair to wash away bad luck||Day 15 of Month 6||Five coloured noodles (yudumyeon), rice dumplings (sudan)|
|Chilseok||Meeting day of Gyeonwoo and Jiknyeo, in Korean folk tale||Fabric weaving||Day 7 of Month 7||wheat pancake (milijeonbyeong), rice cake with red beans (sirutteok)|
|Baekjung||Worship to Buddha||Worship to Buddha||Day 15 of Month 7||mixed rice cake (seoktanbyeong)|
|Chuseok||Harvest festival||Visit to ancestral grave, ssireum, offering earliest rice grain (olbyeosinmi), circle dance (ganggang suwollae)||Day 15 of Month 8||pine flavoured rice cake stuffed with chestnuts, sesame or beans (songpyeon), taro soup (torantang)|
|Jungyangjeol||Migrant sparrows leave||Celebrating autumn with poetry and painting, composing poetry, enjoying nature.||Day 9 of Month 9||chrysanthemum pancake (gukhwajeon), roe (eoran), honey citron tea (yujacheong)|
|Dongji||Winter Solstice||Rites to dispel bad spirits||Around December 22 in the solar calendar||redbean soup with rice dumplings (patjuk)|
|Seotdal Geumeum||New Year's Eve||Staying up all night long with all doors open to receive ancestral spirits||Last day of Month 12||mixed rice with vegetables (bibimbap), bean powder rice cakes (injeolmi), traditional biscuits (hangwa)|
There are also many regional festivals celebrated according to the lunar calendar.
See also 
- Pyeon, Prof. M. Y. The Folkloric Study of Chopail (Buddha's Birthday). Seoul: Minsokwon, 2002.