Vietnamese Lunar Calendar
Convert any date between the solar (Gregorian) and the Vietnamese lunar calendar, browse a month grid with lunar days, and see the can chi names of today. Everything is calculated in your browser using astronomical formulas, so it works offline.
How the Vietnamese lunar calendar works
The Vietnamese calendar is lunisolar. Each month begins on the day of the new moon, so a month lasts 29 or 30 days, while the year is kept in step with the seasons through the sun. A common year has 12 months, which is about 354 days, roughly 11 days shorter than a solar year.
To find the new moon day and the sun's position, this tool uses astronomical formulas based on Jean Meeus, evaluated for the Vietnamese time zone, UTC+7. The day of the new moon is the calendar day, in that zone, on which the moon and sun line up. Month 11 is defined as the month that contains the winter solstice, and every other month is numbered from it.
Leap months
Twelve lunar months fall short of a solar year, so about every three years a thirteenth month is inserted. The sun passes twelve major solar terms, one every 30 degrees of its path. A normal month contains one of them. The first month in a 13-month year that contains none becomes the leap month and takes the number of the month before it. Recent examples are the leap months 4 in 2020, 2 in 2023 and 6 in 2025. Tick the leap month box in the converter to enter one.
Why Vietnam and China sometimes differ
Vietnam keeps UTC+7 and China uses UTC+8. When a new moon happens within an hour of midnight, the two countries put it on different days, and month boundaries and the leap month can shift with it. Tết in 1985 fell on 21 January in Vietnam but 20 February in China. In 2007 Vietnamese Tết was 17 February and Chinese New Year was 18 February. The same effect applies to 2030: the new moon is at 23:08 Vietnamese time on 2 February, so Vietnam celebrates Tết on 2 February.
The can chi cycle
Years, months and days are named by pairing one of ten heavenly stems (Giáp, Ất, Bính, Đinh, Mậu, Kỷ, Canh, Tân, Nhâm, Quý) with one of twelve earthly branches (Tý, Sửu, Dần, Mão, Thìn, Tỵ, Ngọ, Mùi, Thân, Dậu, Tuất, Hợi). The pairs repeat every 60 steps. The branches match the twelve zodiac animals, so 2026 is Bính Ngọ, the Year of the Horse. The calendar here shows these names for today and for any date you convert, and nothing more is claimed about them: it is a naming system, not a forecast.
Frequently asked questions
Why is Tết on a different solar date every year?
Tết is the first day of the first lunar month, and lunar months follow the moon, so the date moves between 21 January and 20 February in the solar calendar.
Is this the same as the Chinese calendar?
Mostly yes, but the Vietnamese version is computed for UTC+7 instead of UTC+8, so a few new moons, and sometimes a leap month, land on different days.
How accurate is the conversion?
Tết 1985 and 2000 to 2040, and the leap months we checked, match published calendars. Other years use the same astronomical method and may rarely differ from official calendars.
What does a leap month look like in the converter?
It has the same number as the month before it and is marked as leap. For example 2023 has a leap month 2, so there are two months numbered 2.
Does it work offline?
Yes. All calculations run in your browser and no date you enter is sent anywhere.