Korean, Chinese and Vietnamese Lunar Calendars
China, Korea and Vietnam use the same kind of lunisolar calendar for festivals, ancestral rites and lunar birthdays, yet the Chinese New Year, the Korean Seollal and the Vietnamese Tết do not fall on the same day in every year. This guide explains why, with the dates where the three calendars part ways.
How a Lunar Month and Year Are Made
A month of these calendars begins on the day of the new moon (朔), the moment when the Moon is in line with the Sun. Months are therefore 29 or 30 days long, and twelve of them make about 354 days, roughly 11 days less than a solar year.
To keep the months in step with the seasons, the calendar uses the Sun as well. The month that contains the winter solstice is month 11. When there are 13 new moons from one winter solstice to the next, one month becomes a leap month: the first month that contains none of the twelve principal solar terms (中气), the points where the Sun's longitude is a multiple of 30 degrees. A leap month repeats the number of the month before it, so a year can have month 4 followed by leap month 4.
The lunar new year is the first day of month 1, two months after the month of the winter solstice, or three when a leap month falls in between. It falls between late January and late February.
Why the Same Rules Give Different Dates
The new moon happens at the same moment for the whole world, but the calendar day on which it falls depends on the clock. China counts in China Standard Time (UTC+8), Korea in Korea Standard Time (UTC+9), and Vietnam, for its lunar calendar, in UTC+7. A new moon at 23:30 in Beijing is at 00:30 the next day in Seoul and at 22:30 in Hanoi, so the month starts on different days.
| Lunar date | China | Korea | Vietnam |
|---|---|---|---|
| New year 1968 | 30 January | 30 January | 29 January |
| New year 1985 | 20 February | 20 February | 21 January |
| New year 1997 | 7 February | 8 February | 7 February |
| New year 2007 | 18 February | 18 February | 17 February |
| Month 9, day 1 of 2026 | 10 October | 11 October | 10 October |
| New year 2027 | 6 February | 7 February | 6 February |
| New year 2030 | 3 February | 3 February | 2 February |
Between 1901 and 2050 the Korean and Chinese tables start a month on different days 62 times; each time the Korean month begins one day later. The new year itself differs in nine of those years: 1916, 1944, 1954, 1958, 1966, 1988, 1997, 2027 and 2028. Vietnam and China start a month on different days 30 times between 1968 and 2050, and their new years differ in 1968, 1969, 1985, 2007 and 2030.
When the Leap Month Moves
A shifted new moon can also change which month lacks a principal solar term, and so move the leap month. In 2012 the Korean calendar had a leap month 3 and the Chinese a leap month 4; in 2017 Korea had leap month 5 and China leap month 6.
The largest gap of the period came in 1984 and 1985. China inserted a leap month 10 at the end of 1984, while the Vietnamese calendar had no leap month that year and a leap month 2 in 1985 instead. As a result Vietnamese Tết fell on 21 January 1985, a whole month before the Chinese New Year of 20 February.
Where the Dates Come From
- Korea: the Korea Astronomy and Space Science Institute (KASI) publishes the official conversion. Its dates are consistent with UTC+8 before 1912, UTC+9 from 1912, UTC+8:30 from 21 March 1954 and UTC+9 again from 10 August 1961, the standard times Korea used.
- China: the Hong Kong Observatory publishes day-by-day tables of the Gregorian and lunar dates from 1901 to 2100.
- Vietnam: the converter calculates the months for UTC+7 from 1968 and uses the Chinese dates before 1968.
The converter holds every Korean month from KASI and every Chinese month from the Hong Kong Observatory between 1901 and 2050, and unit tests compare each of them. The Vietnamese months are calculated with an astronomical method that reproduces all 1,867 KASI months from 1900 to 2050 and every Hong Kong Observatory month from 1929, and they match the Vietnamese government's notice of Tết 2025.
Lunar Birthdays and Anniversaries
- A lunar birthday or memorial day moves every year in the Gregorian calendar, so convert it for the year you need.
- Someone born in a leap month usually keeps the birthday on the ordinary month of the same number, because most years have no such leap month.
- If the birthday is on day 30 and the month has only 29 days that year, it is commonly kept on day 29.
- Check that you use the calendar of the right country. A family in Korea follows the Korean date, which can be a day later than a Chinese calendar printed abroad.
The Zodiac Year
Each lunar year has a sexagenary name, a pair of one of ten heavenly stems and one of twelve earthly branches: 2026 is 丙午, the year of the horse. In the calendars the year and its animal change at the lunar new year; saju, Chinese astrology and some almanacs change it at 立春, the start of spring around 4 February. Vietnam's zodiac has the cat instead of the rabbit and the buffalo instead of the ox.
Frequently Asked Questions
Is the Korean lunar calendar the same as the Chinese one?
The rules are the same, but the dates are worked out for Korean time, so about once every two or three years a month starts a day later in Korea. Leap months can differ too, as in 2012 and 2017.
Why was Vietnamese Tết a month earlier in 1985?
Because the leap month fell in different years: China had a leap month 10 at the end of 1984, Vietnam a leap month 2 in 1985. Tết was on 21 January 1985 and the Chinese New Year on 20 February.
Does the lunar calendar change every year?
Yes. Each year has its own month lengths and, in some years, a leap month, so lunar dates fall on different Gregorian days every year.
Is the Japanese old calendar (旧暦) included?
No. The converter covers the Korean, Chinese and Vietnamese calendars only.
Sources
Source: 한국천문연구원 천문우주지식정보: 음양력 변환 · Last checked:
Source: 香港天文台: 公曆與農曆日期對照表 · Last checked:
Source: Cổng TTĐT Chính phủ: Lịch nghỉ Tết Nguyên đán Ất Tỵ 2025 · Last checked: