Months in Vietnamese: twelve numbered months, lunar names and dates

Month plus number: how the months in Vietnamese are built

Vietnamese counts the months the way it counts the weekdays. Tháng means month, and the number after it says which one: tháng hai is the second month, tháng chín the ninth. Anyone who can count to twelve already knows the months in Vietnamese, and the digit form is just as regular. The Unicode CLDR data that software uses has no month names for Vietnamese at all, only tháng 1 to tháng 12 in full and thg 1 to thg 12 abbreviated.

Two numbers change shape. April is tháng tư, with the Sino-Vietnamese tư in place of the counting word bốn; Wiktionary lists tháng bốn as a synonym that is heard much less often. November keeps một unchanged: it is tháng mười một, eleven, because the form mốt replaces một only from twenty-one upward. A learner who says tháng mười mốt has applied the rule one decade too early; among the months in Vietnamese, November is the only place where that slip can happen.

Word order matters. Tháng hai is February, the second month, while hai tháng, with the number first, means two months as a length of time. The same swap separates tháng năm, May, from năm tháng, five months, and since năm also means year, the context has to do some of the work.

Tháng giêng, tháng chạp and the lunar calendar

Vietnam has used the Gregorian calendar officially since 1954, and a decree of 8 August 1967 in North Vietnam made it the sole official calendar. The lunisolar calendar, âm lịch, kept its place for festivals and commemorations, above all Tết Nguyên Đán, the lunar new year, and Tết Trung Thu, the mid-autumn festival.

That calendar is where the two named months live. Tháng giêng is the first lunar month, the month of Tết; Wiktionary traces giêng to a non-Sino-Vietnamese reading of the Chinese 正 in 正月, the principal month. Tháng chạp is the twelfth and last lunar month, the month that closes the old year.

The numbered names serve the lunar year too, and one of them is ambiguous. Wiktionary gives tháng một two meanings: January in the Gregorian calendar and the eleventh month of the lunar year. Some printed calendars blur the line the other way and use tháng giêng for January, a usage Wiktionary records as an extension of the lunar term. On a calendar that shows both systems, the small lunar date under each Gregorian day is the safe guide.

Writing a date: day, month, year

Vietnamese puts the day first, then the month, then the year, and names each part: ngày 28 tháng 10 năm 2026 is 28 October 2026, word for word day 28 month 10 year 2026. In figures the same order gives 28/10/2026. CLDR's patterns for software are shorter: the long date reads 28 tháng 10, 2026, and the short one 28/10/26.

Official papers follow Decree 30/2020/NĐ-CP on clerical work, which sets the form of the issue date at the head of a document. Days below 10 and the months January and February take a leading zero, as in ngày 08 tháng 02, so that no one can add a digit later. March to December are written without one.

The same decree regulates capitals when a month is written out in words: only the number syllable is capitalised, as in tháng Năm or tháng Tám. Elsewhere lower case is common, and the cross-language months table writes all twelve that way.

Pronouncing the months: tone marks to watch

Tháng carries the rising sắc tone, so every month starts on a rising syllable before the number. The numbers keep their own tones: một has the heavy nặng tone with its dot below, bảy the dipping hỏi tone, and mười a low falling huyền tone. In the Hanoi transcriptions on Wiktionary, mười is [mɨəj˨˩] with a glide, and Saigon speech reduces the vowel to [mɨj˨˩].

Southern speakers also turn final -t into -k in một, which Wiktionary's Saigon transcription of tháng một gives as [tʰaːŋ˦˥ mok̚˨˩˨], and pronounce the ch of chín as a plain stop, [c]. The IPA chart explains the symbols, and the numbers in Vietnamese page covers the rules that give một, mốt, tư and lăm their places.