TL;DR: Tiểu Mãn is the 8th of the 24 solar terms, beginning when the Sun reaches 60 degrees of ecliptic longitude measured from the vernal equinox, which in these years falls on 20 or 21 May (in 2026 at 07:28 on 21 May, Vietnam time), and lasting until around 5 or 6 June, when Mang Chủng begins. It is the principal term of the fourth lunar month. In Vietnam the name is usually explained as "small flood": early summer showers raise rivers and streams in the North to a moderate, not yet great, level; classical Chinese texts explain it as living things growing by this time to a slight fullness. It is a calendrical marker used for farming and crop care, not a fixed festival with its own rites.
What is Tiểu Mãn?
Tiểu Mãn is the 8th of the 24 solar terms of the year. It follows Lập Hạ and ends around 5 or 6 June on the Gregorian calendar, when the Mang Chủng term begins[1]. It is one marker within the system of 24 solar terms, that is, 24 periods of time, each lasting 15 or 16 days, describing 24 different weather phases of the year according to the Earth's position in its orbit[1].
In 2026, Tiểu Mãn begins at 07:28 on 21 May (Vietnam time), which is the 5th day of the fourth lunar month of the year Bính Ngọ, an Ất Mùi day, and it ends when Mang Chủng begins at 22:37 on 5 June. In Vietnam time, from 1900 to 2100 the opening day of Tiểu Mãn falls on 20, 21 or 22 May; from 2000 to 2100 it falls only on 20 or 21 May.
When does Tiểu Mãn begin, and how is it calculated?
Tiểu Mãn begins when the Sun reaches 60 degrees of ecliptic longitude, taking the vernal equinox as the zero point at 0 degrees[1]. This method is based on the actual position of the Sun rather than on a fixed date printed in advance in a calendar, so the date and hour of the term shift from year to year.
The table below gives the moment Tiểu Mãn begins from 2025 to 2030, in Vietnam time, with the lunar date.
| Year | Gregorian date | Time the term begins | Lunar date |
|---|---|---|---|
| 2025 | 21 May | 01:42 | 24th day, fourth month, Ất Tỵ |
| 2026 | 21 May | 07:28 | 5th day, fourth month, Bính Ngọ |
| 2027 | 21 May | 13:14 | 16th day, fourth month, Đinh Mùi |
| 2028 | 20 May | 19:01 | 26th day, fourth month, Mậu Thân |
| 2029 | 21 May | 00:48 | 9th day, fourth month, Kỷ Dậu |
| 2030 | 21 May | 06:37 | 20th day, fourth month, Canh Tuất |
What does the name "Tiểu Mãn" mean?
According to the common explanation in Vietnam, Tiểu Mãn means "small flood"[1]. This is the point when the drought and water shortage caused by the hot, muggy spells of Lập Hạ come to an end, showing that water has become more plentiful[1]. During this period, water in the rivers and streams of the North rises, but on a small to moderate scale, caused by the rain showers of the term[1].
Classical Chinese texts explain the name through plants rather than water. Tuế thời quảng ký by Trần Nguyên Tịnh of the Southern Song, under the first month of summer, quotes the Tam thống lịch: "小滿為四月中氣，小滿者言物長於此小得盈滿", meaning that Tiểu Mãn is the principal term of the fourth month, and it is called Tiểu Mãn because living things grow by this time to a slight fullness[3]. The same section quotes the Chu thư Thời huấn, which divides the term into three five-day periods: "小滿之日苦菜秀，後五日靡草死，後五日麥秋至", that is, on the day of Tiểu Mãn the bitter herb flowers, five days later the soft grasses wither, and five days after that the wheat ripens[3]. This is a Chinese book on the calendar and seasonal signs, not a record of Vietnamese customs.
Does Tiểu Mãn have customs of its own?
Tiểu Mãn is not a fixed festival with its own rituals like Tết Nguyên Đán or Tết Đoan Ngọ. Dương Bá Trạc in Gia lễ giản yếu (1932) writes that meaningless festival days such as Đoan Ngọ, Thượng Nguyên, Trung Nguyên and Trung Thu "should all be dropped", and that only on Tết Nguyên Đán, Tết Thanh Minh and Tết Cơm Mới should one remember to make offerings to the ancestors[4]. Tiểu Mãn is not among the days mentioned there[4]. The first-month-of-summer section of Tuế thời quảng ký likewise records only the calendar and seasonal signs for Tiểu Mãn, and no rite tied to this day[3].
In Vietnam, Tiểu Mãn is therefore used mainly as a calendrical marker and a weather marker, not as an occasion for offerings. This differs from Thanh Minh, the solar term tied to the custom of tending graves.
In folk experience, Tiểu Mãn is regarded as an important time for tending crops and fruit, because living creatures and microorganisms grow very strongly in this period and can harm crops, so farmers need to monitor, water and prune more frequently[1]. This is also the time when both temperature and humidity rise high, so many people need to pay attention to their health in order to avoid a number of illnesses characteristic of this season[1].
What did people of earlier times use Tiểu Mãn for?
Beyond farming, solar terms also serve as markers by which divination arts divide time.
In Bát Tự, months are counted from the terms that open them, not from the principal terms: the Tỵ month opens at Lập Hạ and ends at Mang Chủng, while Tiểu Mãn is the principal term in the middle of the Tỵ month and does not change the month pillar. People born before or after the moment Tiểu Mãn begins in 2026 both have the month pillar Quý Tỵ.
The book Trạch vận tân án, in its section on calculating fortune by year and month, pairs Lập Hạ with Tiểu Mãn as one month, for example "18th of the Third Month to the 19th of the Fourth Month, within the Lập Hạ Tiểu Mãn term, year Bích month Bích"[5]. This way of recording also treats the month as opening at Lập Hạ, with Tiểu Mãn falling inside the month rather than opening a new one.
Kỳ Môn Độn Giáp divides each solar term into three cycles and takes the first day of each cycle (the phù đầu) from the stem and branch of the day. The book Kỳ Môn Chỉ Quy writes that the phù đầu of the three cycles are fixed while the solar terms of the four seasons are not, so the methods of siêu thần, tiếp khí, chiết cục, bổ cục and nhuận cục must be used: siêu thần is when the phù đầu arrives before the solar term, tiếp khí is when the solar term arrives before the phù đầu and the configuration of the lower cycle must be borrowed to bridge the gap, and nhuận cục is supplying the remaining surplus time[2].
Why do solar terms not coincide with lunar months?
Solar terms and lunar months are two different systems of counting time, running in parallel. The lunar month follows the moon's phases; the solar terms follow the Sun's position on the ecliptic[1]. Each lunar month lasts about 29.5 days, so a lunar year is shorter than a solar year by roughly 11 days; to keep the terms from drifting out of their seasons, the calendar must add leap months.
The two systems are tied together by the principal terms. Tiểu Mãn is a principal term (a solar longitude that is a multiple of 30 degrees), and the lunar month containing Tiểu Mãn is the fourth month; in a year of 13 months, the first month containing no principal term is the leap month. That is why the lunar date of Tiểu Mãn shifts within the fourth month, from the 5th to the 26th in the years of the table above.
How does Tiểu Mãn differ from Lập Hạ and Mang Chủng?
The three consecutive terms Lập Hạ, Tiểu Mãn and Mang Chủng mark three stages of early summer. Lập Hạ means "beginning of summer", opening the summer season[1]. Tiểu Mãn is the time when rain showers make water rise on a small to moderate scale[1]. Mang Chủng is the next term, beginning around 5 or 6 June[1].
These terms are not weather forecasts for a specific day. Saying that today falls within Tiểu Mãn does not mean it will certainly rain today, only that today belongs to the period named Tiểu Mãn.
Is Tiểu Mãn a bad day according to the perpetual calendar?
No. Solar terms and good or bad days are two different matters. On 21 May 2026, the opening day of Tiểu Mãn, the perpetual calendar marks it as a Đạo Tặc day, and folk belief holds this to be a very bad day, unsuitable for travel or for starting major undertakings, saying that on such a day "travel brings harm, loss of property"[1]. But that is the assessment of the good-day bad-day system, tied to the stem and branch of that particular day, not an attribute of the Tiểu Mãn term[1].
The opening day of Tiểu Mãn in another year falls on a different stem and branch, such as a Canh Dần day in 2025 or a Canh Tý day in 2027, so the good or bad label differs too. Seeing the words "Tiểu Mãn" on a calendar sheet does not mean the whole term is good or bad.
Nhật Nguyệt's suggestion
Nhật Nguyệt's suggestion: if you are looking up Tiểu Mãn in order to choose a day for a major undertaking, separate the two questions. The first question is which term that day falls in, which is answered by calendrical method and can be cross-checked against the solar term table of any year. The second question is whether that day is good or bad according to the perpetual calendar, which is answered by the good-day bad-day system, and this is a convention of the books, not an astronomical fact. Do not merge the two questions into one.
