The traditional Korean calendar is a lunisolar calendar, like the traditional calendars of other East Asian countries. Dates are calculated from Korea's meridian (135th meridian east in modern time for South Korea), 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 referred 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 Korean calendar is derived from the Chinese calendar. The traditional calendar designated its years via Korean era names from 270 to 963, then Chinese era names with Korean era names were used a few times until 1894. In 1894 and 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 has only been occasionally used since 1961, and mostly in North Korea prior to 1997.
Although not being an official calendar, in South Korea, the traditional Korean calendar is still maintained by the government. The current version is based on China's Shixian calendar ("siheonnyeok 시헌력(時憲暦)" in Korean), which was in turn developed by Jesuit scholars. However, because the Korean calendar is now based on the moon's shape seen from Korea, occasionally the calendar diverges from the traditional Chinese calendar by one day, even though the underlying rule is the same. As a result, sometime the New Year's Day differ by one between the two countries, which last happened in 1997.
Note that traditional Korean calendar has no concept of "weekdays": the following are names of weekdays in the modern (Western) calendar.
In modern Korean language, the months of both the traditional lunisolar and Western calendars are named by prefixing Sino-Korean numerals to wol, the Sino-Korean word for "month". Traditionally, when speaking of individuals' birth months, the months of the lunisolar calendar were named by prefixing the native Korean name of the animal associated with each Earthly Branch in the Chinese zodiac to dal, the native Korean word for "month". Additionally, the first, eleventh, and twelfth months have other Korean names which are similar to traditional Chinese month names. However, the other traditional Chinese month names, such as Xìngyuè ("apricot month") for the second month, are not used in Korean.
|Modern name||Traditional name||Notes|
|Month 1||1월 (일월)||Ilwol||Tiger Month||호랑이달||Horangidal|
|Primary Month||정월 (正月)||Jeong-wol||A loanword from Chinese Zhēngyuè|
|Month 2||2월 (이월)||Iwol||Rabbit Month||토끼달||Tokkidal|
|Month 3||3월 (삼월)||Samwol||Dragon Month||용달||Yongdal|
|Month 4||4월 (사월)||Sawol||Snake Month||뱀달||Baemdal|
|Month 5||5월 (오월)||Owol||Horse Month||말달||Maldal|
|Month 6||6월 (유월)||Yuwol||Goat Month||양달||Yangdal|
|Month 7||7월 (칠월)||Chilwol||Monkey Month||원승이달||Wonseung-idal|
|Month 8||8월 (팔월)||Palwol||Rooster Month||닭달||Dakdal|
|Month 9||9월 (구월)||Guwol||Dog Month||개달||Gaedal|
|Month 10||10월 (시월)||Siwol||Pig Month||돼지달||Dwaejidal|
|Month 11||11월 (십일월)||Sibilwol||Rat Month||쥐달||Jwidal|
|Winter Solstice Month||동짓달||Dongjitdal||Compare Chinese Dōngyuè, "Winter Month"|
|Month 12||12월 (십이월)||Sibiwol||Ox Month||소달||Sodal|
|섣달||Seotdal||Compare Chinese Làyuè, "preservation month"|
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.
|Seollal (설날)||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 neighbors; bows to elders (sebae, 세배, 歲拜), yut nori (윷놀이).||Day 1 of Month 1||rice cake soup (tteokguk, 떡국), honey cakes (yakgwa, 약과, 藥果).|
|Daeboreum (대보름, 大보름)||First full moon||Greeting of the moon (dalmaji, 달맞이), kite-flying, burning talismans to ward off evil spirits (aengmagi taeugi, 액막이 태우기), bonfires (daljip taeugi, 달집 태우기)||Day 15 of Month 1||rice boiled with five grains (ogokbap, 오곡밥, 五穀-), eating nuts, e.g. walnuts, pine nuts, peanuts, chestnuts (bureom, 부럼), wine drinking (gwibalgisul)|
|Meoseumnal (머슴날)||Festival for servants||Housecleaning, coming of age ceremony, fishermen's shaman rite (yeongdeunggut, 영등굿)||Day 1 of Month 2||stuffed pine-flavored rice cakes (songpyeon, 송편)|
|Samjinnal (삼짇날)||Migrant swallows return||Leg fighting, fortune telling||Day 3 of Month 3||azalea wine (dugyeonju, 두견주, 杜鵑酒), azalea rice cake (dugyeon hwajeon, 두견화전, 杜鵑花煎)|
|Hansik (한식, 寒食)||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, 쑥떡), mugwort dumplings (ssukdanja, 쑥단자), mugwort soup (ssuktang, 쑥탕)|
|Chopail (釋迦誕生日)||Buddha's birthday||Lotus Lantern festival||Day 8 of Month 4||rice cake (jjintteok, 찐떡), flower rice cake (hwajeon, 화전, 花煎)|
|Dano (단오, 端午, or 수릿날）||Spring festival||Washing hair with iris water, wrestling (ssireum, 씨름), swinging, giving fans as gifts||Day 5 of Month 5||rice cake with herbs (surichwitteok, 수리취떡), herring soup (junchiguk, 준치국)|
|Yudu (유두, 流頭)||Water greeting||Water greeting, washing hair to wash away bad luck||Day 15 of Month 6||Five coloured noodles (yudumyeon, 유두면), cooked rice cake (sudan, 수단, 水團)|
|Chilseok (칠석, 七夕)||Meeting day of Gyeonwoo and Jiknyeo, in Korean folk tale||Fabric weaving||Day 7 of Month 7||wheat pancake (miljeonbyeong, 밀전병), steamed rice cake with red beans (sirutteok, 시루떡)|
|Baekjung (백중, 百中)||Worship to Buddha||Worship to Buddha||Day 15 of Month 7||mixed rice cake (seoktanbyeong, 석탄병, 惜呑餠)|
|Chuseok (추석, 秋夕)||Harvest festival||Visit to ancestral grave, ssireum, offering earliest rice grain (olbyeosinmi, 올벼신미, --新味), circle dance (ganggang sullae, 강강술래)||Day 15 of Month 8||pine-flavored rice cake stuffed with chestnuts, sesame or beans (songpyeon, 송편), taro soup (torantang, 토란탕)|
|Jungyangjeol (중양절, 重陽節)||Migrant sparrows leave||Celebrating autumn with poetry and painting, composing poetry, enjoying nature.||Day 9 of Month 9||chrysanthemum pancake (gukhwajeon, 국화전, 菊花煎), fish roe (eoran, 어란, 魚卵), honey citron tea (yujacheong, 유자청, 柚子淸)|
|Dongji (동지, 冬至)||Winter Solstice||Rites to dispel bad spirits||Around December 22 in the solar calendar||red bean porridge with rice dumplings (patjuk, 팥죽)|
|Seotdal Geumeum (섣달그믐)||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, 비빔밥), bean powder rice cakes (injeolmi, 인절미), traditional biscuits (hangwa, 한과, 韓菓)|
There are also many regional festivals celebrated according to the lunar calendar.