Lịch Âm Việt
Vietnamese vs Chinese Lunar Calendar: Why Tết Can Differ
· 4 min read
The Vietnamese and Chinese lunar calendars use the same rules. The one difference is the clock: Vietnam computes its calendar in Hanoi time (UTC+7), China in Beijing time (UTC+8). That single hour is enough to put the first day of some months a day apart, and, rarely, to shift a leap month so that Tết falls a whole month apart, as happened in 1985.
This matters if you use a Chinese lunar calendar to track a Vietnamese giỗ (death anniversary) or Tết. Most years it matches. Some years it doesn’t.
Same rules on both sides
The lunisolar calendar both countries use today is astronomical:
- The first day of a month (mùng 1) is the day on which the new moon occurs.
- The 11th lunar month always contains the winter solstice.
- In a year with 13 months, the first month that contains no “major solar term” becomes the leap month (more on solar terms in the 24 solar terms).
Everything depends on which day the new moon falls on, and “which day” depends on whose clock you use.
How one hour shifts a whole day
Say a new moon happens at 23:30 Hanoi time on 1 February. In Beijing it is already 00:30 on 2 February. So:
- Vietnamese calendar: the new month starts on 1 February.
- Chinese calendar: the new month starts on 2 February.
This only happens when the new moon falls between 23:00 and midnight Vietnam time, so it isn’t frequent, but it comes up a few times per decade.
Tết dates that differed
Computed with this site’s lunar calendar library, using UTC+7 and UTC+8:
| Year | Tết in Vietnam | Chinese New Year |
|---|---|---|
| 1968 | Monday, 29 January 1968 | Tuesday, 30 January 1968 |
| 1985 | Monday, 21 January 1985 | Wednesday, 20 February 1985 |
| 2007 | Saturday, 17 February 2007 | Sunday, 18 February 2007 |
| 2030 | Saturday, 2 February 2030 | Sunday, 3 February 2030 |
1968 was the first year North Vietnam used a calendar computed for UTC+7, so the Tết of Mậu Thân came a day earlier in the North than in places still using the older calendar.
In recent and coming years the two match: Tết 2026 was on 17 February in both, and Tết 2027 is on Saturday, 6 February 2027 in both. The next split is 2030.
It’s not only Tết. The first day of other months can differ too. For example, 14 December 2020 was the 1st day of the 11th month in Vietnam, but still the 30th day of the 10th month in China.
1985: a whole month apart
This is the case people remember. Late in 1984 a new moon fell in that sensitive hour, the two calendars counted months differently, and the leap month ended up in different places:
| Solar date | Vietnamese calendar | Chinese calendar |
|---|---|---|
| 23 Nov 1984 | 1st of month 11 | 1st of leap month 10 |
| 22 Dec 1984 | 1st of month 12 | 1st of month 11 |
| 21 Jan 1985 | Tết, year Ất Sửu | 1st of month 12 |
| 20 Feb 1985 | 1st of month 2 | New Year, year Ất Sửu |
| 21 Mar 1985 | 1st of leap month 2 | 1st of month 2 |
China had a leap 10th month in 1984; Vietnam had a leap 2nd month in 1985. From March 1985 the months lined up again, but Tết had already been a month apart.
In practice, someone born between 21 January and 19 February 1985 was born in the year Ất Sửu (Buffalo) by the Vietnamese calendar, but still in Giáp Tý (Rat) by the Chinese one. If you look up a birth year in a Chinese source, this is where mistakes happen.
What never differs
- The Can Chi of a day runs in an unbroken 60-day cycle, regardless of months, so a given solar date has the same day name in both countries. For example, 17 October 2026 is a Giáp Tý day in both. See Can Chi explained.
- Solar terms can differ by a day when the moment falls close to midnight, but that’s rare.
- The year’s Can Chi only differs in the window where the two New Years fall apart.
The zodiac animals differ a little
The 12 earthly branches are the same, but two animals are read differently in Vietnam: Mão is the Cat, not the Rabbit, and Sửu is usually the Buffalo (water buffalo) rather than the Ox. So 2023 (Quý Mão) was the Year of the Cat in Vietnam.
What this means for your giỗ
If you track a Vietnamese death anniversary with a Chinese lunar calendar, it will be right most years and occasionally a day off, or in a year like 1985, a month off. For family dates, use a calendar computed for Vietnam.
Lịch Âm Việt and the calendar pages on lichamviet.com are computed in UTC+7, like Vietnam’s official calendar. How to set a yearly reminder: death anniversary reminders by lunar date. To look up any date, use the solar to lunar converter (in Vietnamese) or the 2027 lunar calendar (in Vietnamese).
FAQ
Why is Tết sometimes on a different day from Chinese New Year?
Both calendars follow the same astronomical rules, but Vietnam counts days in UTC+7 and China in UTC+8. When a new moon falls between 23:00 and midnight Vietnam time, the first day of the month differs by one day between the two countries.
How far apart were Tết and Chinese New Year in 1985?
A whole month. Vietnam celebrated Tết on 21 January 1985, China on 20 February 1985, because the two calendars placed the leap month in different places.
When will they differ next?
In 2030: Tết in Vietnam is on 2 February 2030 and Chinese New Year on 3 February 2030, according to the calendar library used on this site.
Which time zone does Lịch Âm Việt use?
Vietnam time, UTC+7, matching Vietnam's official calendar.
Is the Vietnamese zodiac different too?
Slightly. The Vietnamese zodiac has the Cat instead of the Rabbit and the Buffalo for the Ox year. The Can Chi year names follow the same 60-year cycle in both countries.
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