Lunar Calendar vs Solar Calendar

The fundamental difference between lunar and solar calendars comes down to what they track. A solar calendar counts the Earth's orbit around the Sun: one year equals one orbit (≈365.25 days). A lunar calendar counts cycles of the Moon: one month equals one synodic cycle (≈29.53 days). Twelve lunar months add up to only about 354 days — roughly 11 days shorter than the solar year — which causes lunar dates to drift steadily through the solar calendar.

Use Lunar Solar to convert between Korean lunar (음력) and Gregorian dates for any date from 1900 to 2050.

The Intercalary Month Solution

Pure lunar calendars (like the Islamic Hijri calendar) let holidays drift through all seasons over a 33-year cycle. Lunisolar calendars — used in Korea, China, and traditionally in Judaism — add an intercalary (leap) month roughly every three years to keep the lunar calendar approximately aligned with the solar year. The Korean and Chinese systems follow a 19-year Metonic cycle that inserts 7 extra months per cycle.

The 24 Solar Terms

East Asian agricultural practice relies not on lunar months but on the 24 solar terms (이십사절기), points in the solar year at which the Sun reaches specific ecliptic longitudes. Dates like Dongji (winter solstice) and Ipchun (start of spring) are solar-year events, not lunar ones. This shows that traditional East Asian timekeeping was always hybrid — lunar for social events, solar for farming.

Holiday Drift in Practice

Chuseok (추석, Korean harvest festival) falls on the 15th day of the 8th lunar month. In the Gregorian calendar, this lands anywhere from mid-September to mid-October depending on the year. Seollal (설날, Lunar New Year) similarly moves. Workers and businesses in Korea must check the government-issued lunar calendar each year to plan holiday travel.

When Each Calendar Matters

• Official legal and business matters: always use the Gregorian solar calendar.
• Traditional holidays, ancestral rites (제사), and astrological traditions: use the lunar calendar. Korean families observe death anniversaries on the lunar date the person died, which means the Gregorian date of the memorial shifts year to year.
• Agricultural traditions: use solar terms, which are solar-year derived despite their traditional context.

Understanding the distinction prevents confusion when Korean relatives specify a ceremony date using only the lunar month and day.