Lunar Calendar Converter
Convert between solar and Vietnamese lunar dates, with can chi and solar terms.
Dates are converted entirely in this page. Nothing is sent or stored anywhere.
The Vietnamese lunar calendar is not the Chinese calendar with different names. Both are lunisolar and both follow the same rules - a month begins on the day of the new moon, the month containing the winter solstice is month 11, and a year with thirteen lunations repeats the first month after month 11 that contains no major solar term - but Vietnam computes those rules at UTC+7 while China uses UTC+8. Most months the hour makes no difference. Sometimes it moves a new moon across midnight, and the calendars genuinely part ways: in 1985 Vietnam celebrated Tet on 21 January, a full month before China on 20 February.
More about Lunar Calendar Converter
This converter works in both directions between Gregorian and Vietnamese lunar dates for 1900-2199, and shows today's lunar date the moment the page opens. Alongside the date you get the can chi (sexagenary) names for the year, month and day, and the solar term (tiet khi) in force - the details Vietnamese almanacs print beside every date.
Two honest caveats. Vietnam only adopted the UTC+7 calendar on 8 August 1967, and the South kept the old computation until 1975, so dates before then are shown by today's rules, not the calendar people actually lived by. And dates far in the future are astronomical projections. The method implemented here is the algorithm published by Ho Ngoc Duc, the reference for the modern Vietnamese calendar, rebuilt from the underlying astronomical formulas and verified against every lunar month start from 1899 to 2199.
- Solar to lunar and lunar to solar, over the full 1900-2199 range
- Today's lunar date in Vietnam, shown without any input
- Can chi names for year, month and day, plus the day's solar term
- Leap months handled properly: the checkbox only enables when the year has that leap month
- Month lengths (29 or 30 days) shown right in the picker
- Verified against all 3,722 lunar month starts of 1899-2199
How to use it
- 1Read today's lunar date at the top - no input needed.
- 2Pick a solar date to see its lunar equivalent, with can chi and solar term.
- 3Press "Swap direction" to enter a lunar date instead, choosing day, month, year and - when the year has one - the leap month.
- 4Copy the full result with the copy button.
Questions
Why does the Vietnamese lunar date sometimes differ from the Chinese one?
Vietnam fixes the calendar at UTC+7, China at UTC+8, and when a new moon falls close to midnight the extra hour can push it to the next day in one country but not the other, shifting a month boundary. Tet has differed in 1968, 1969, 1985 and 2007; in 1985 the two calendars were a whole month apart.
What is a leap month and when does one occur?
Twelve lunar months are about 11 days shorter than a solar year, so roughly every three years a thirteenth month is inserted. It is the first month after month 11 that contains no major solar term, and it repeats the previous month's number - 2025, for example, has two month 6.
Are dates before 1967 accurate?
They follow today's UTC+7 rules. Before 8 August 1967 the calendar in civil use in Vietnam was computed at UTC+8, and South Vietnam kept that calendar until 1975, so a historical document may name a day that differs by one from what this tool shows.
What are can chi and tiet khi?
Can chi is the 60-unit cycle of ten heavenly stems and twelve earthly branches that names years, months and days - 2025 is At Ty. Tiet khi are the 24 solar terms, positions of the sun 15 degrees apart, that anchor the calendar to the seasons; the winter solstice term fixes month 11.
Where does the algorithm come from?
From the method published by Ho Ngoc Duc, whose calculations are the de-facto reference for the modern Vietnamese calendar, implemented here from the astronomical formulas in Jean Meeus's books and checked against every lunar month start from 1899 through 2199.