When Does Lập Hạ Begin and What Customs Come With It?

What Is Lập Hạ and When Does It Begin?

Lập Hạ (立夏) is the 7th of the 24 solar terms of the year and marks the start of summer. By convention this term begins around 5 or 6 May in the solar calendar, when Cốc Vũ ends^[1], and lasts until Tiểu Mãn begins, around 20 to 22 May. In 2026, Lập Hạ began at 18:35 on 5 May, Vietnam time.

The name "Lập Hạ" means "start of summer", the opening point of the summer season. In the modern calculation, taking the spring equinox as the zero point of solar longitude, the start of Lập Hạ corresponds to a solar longitude of 45 degrees^[2].

A distinction must be drawn between solar terms and ordinary lunar dates. Solar terms are divided by the Earth's position on its orbit around the Sun, so the start date in the solar calendar is fairly stable, while the corresponding lunar date changes each year.

How Is Lập Hạ Calculated?

The 24 solar terms are 24 spans of time, each 15 or 16 days long, describing 24 different weather stages in the year according to the Earth's position on its orbit^[1]. This is a calendrical system originating in ancient China and later widely used in Vietnam and many East Asian countries.

The basic mechanism divides the ecliptic into 24 equal parts of 15 degrees of solar longitude each. The spring equinox (around 20 or 21 March) corresponds to 0 degrees of solar longitude, the summer solstice (around 21 June) to 90 degrees, the autumn equinox (around 22 or 23 September) to 180 degrees, and the winter solstice (around 21 or 22 December) to 270 degrees. Lập Hạ lies between the spring equinox and the summer solstice, at 45 degrees of solar longitude.

Because it is tied to an actual astronomical position, the start date of Lập Hạ in the solar calendar shifts little: from 1900 to 2100 it falls on 5 or 6 May in 189 of 201 years, and on 4 or 7 May in the remaining years.

What Does Lập Hạ Mean in Daily Life and in Divination Arts?

In the agricultural calendar, Lập Hạ signals the shift to hot weather and the start of vigorous growth for crops. It is a marker for farmers to adjust their planting schedule, tend the fields, and prepare for the following terms such as Tiểu Mãn, Mang Chủng, and Hạ Chí.

In Kỳ Môn Độn Giáp, the solar term is the unit of time used to set up a chart. The book Thuật số Lạc Thư (Kỳ Môn Độn Giáp nguyên thủy) places the three terms Lập Hạ, Tiểu Mãn and Mang Chủng in one group, joined to the Tốn trigram in palace 4^[3].

In fate calculation, the solar term is the marker that fixes the birth month. The book Kỳ Môn Chỉ Quy, discussing how solar terms are used in kỳ môn, cites the rule of the fate calculators: a person born in the third lunar month but after Lập Hạ begins must be counted as born in the fourth month, and one born in the fourth lunar month but before Lập Hạ begins is counted as born in the third month^[4]. This is a convention for drawing up a chart, not a scientific claim about destiny.

What Does the Book Tuế thời quảng ký Say About Lập Hạ?

Tuế thời quảng ký (歲時廣記) is a book by Trần Nguyên Tịnh of the Southern Song. It takes the Nguyệt lệnh, the Hiếu kinh vĩ and the Tam thống lịch as its framework, then arranges by month what other books record about the seasonal festivals. The Tứ khố toàn thư edition has 4 volumes, and its summer section contains 50 entries^[5]. It records old Chinese customs, not Vietnamese ones.

Under the first month of summer, the book quotes the Hiếu kinh vĩ: "穀雨後十五日斗指巽為立夏", meaning that fifteen days after Cốc Vũ, when the handle of the Big Dipper points to the Tốn direction, it is Lập Hạ; and the Tam thống lịch: "立夏為四月節", meaning that Lập Hạ is the term of the fourth month^[5]. It also quotes the Chu thư Thời huấn on the three five-day periods of this term: "立夏之日螻蟈鳴", on the day of Lập Hạ the louguo calls, five days later the earthworms come out, and five days after that the wanggua plant sprouts^[5].

What Customs Belong to the Day of Lập Hạ?

In China, folk customs on the day of Lập Hạ differ by region. The custom of weighing people found in some places comes with the belief that being weighed on this day keeps one healthy through the summer.

In Vietnam, Lập Hạ is known mainly as a marker of the change of season in the lunar calendar, with few customs tied specifically to this day as in China. Vietnamese people usually notice Lập Hạ through daily lunar calendar pages, where the start date of the term is recorded along with can chi information and auspicious or inauspicious days in the vạn niên calendar.

In the vạn niên calendar, each day within Lập Hạ is recorded with its lunar date and the can chi of the day, month, and year. For example, 5 May 2026 is the 19th day of the third lunar month, day Kỷ Mão, month Nhâm Thìn, year Bính Ngọ; 20 May 2026 is the 4th day of the fourth lunar month, day Giáp Ngọ, month Quý Tỵ, year Bính Ngọ.

Quick Reference Table for Lập Hạ Across Years

The table below gives the moment Lập Hạ begins and the moment Tiểu Mãn begins (which is also when Lập Hạ ends) from 2025 to 2030, in Vietnam time (UTC+7).

How Does Lập Hạ Differ from Major Festivals in Vietnam?

Lập Hạ is not a major festival in Vietnam. It is a marker in the system of 24 solar terms, used mainly in the agricultural calendar and in divination arts such as tử bình, kỳ môn, and feng shui. In everyday life, Vietnamese people rarely hold a separate ceremony for this day, unlike occasions such as Tết Nguyên Đán, Tết Đoan Ngọ, or Tết Trung Thu.

However, because Lập Hạ is tied to the change of season, it is still mentioned in daily lunar calendar pages and in calendar lookup apps. Those interested in divination arts often use the day the term begins to determine the birth month in tử bình, or to select dates by the methods of the school they follow.