Solar terms and the Month Pillar: why BaZi months do not begin on lunar day one
BaZi months change at the twelve jie boundaries: Li Chun starts the first month and Jing Zhe the second. Neither lunar day one nor the first day of a calendar month sets this boundary. Births near a solar-term transition need particular care.
The principle in one sentence
In BaZi, the birth month is determined by the Sun's solar-term position, not the calendar's month number. Each jie boundary changes the Month Pillar; Li Chun also changes the Year Pillar.
Jie and qi within the twenty-four solar terms
The twenty-four solar terms alternate between twelve jie and twelve qi. Starting with Li Chun, odd-numbered terms are jie, including Jing Zhe and Qing Ming; the intervening qi include Yu Shui, Chun Fen and Gu Yu. Only the jie boundaries change the Month Pillar.
| Month Branch | BaZi month | Starting jie | Approximate Gregorian date |
|---|---|---|---|
| Yin (寅) | First month | Li Chun — Beginning of Spring | Around February 4 |
| Mao (卯) | Second month | Jing Zhe — Awakening of Insects | Around March 6 |
| Chen (辰) | Third month | Qing Ming — Clear and Bright | Around April 5 |
| Si (巳) | Fourth month | Li Xia — Beginning of Summer | Around May 6 |
| Wu (午) | Fifth month | Mang Zhong — Grain in Ear | Around June 6 |
| Wei (未) | Sixth month | Xiao Shu — Minor Heat | Around July 7 |
| Shen (申) | Seventh month | Li Qiu — Beginning of Autumn | Around August 8 |
| You (酉) | Eighth month | Bai Lu — White Dew | Around September 8 |
| Xu (戌) | Ninth month | Han Lu — Cold Dew | Around October 8 |
| Hai (亥) | Tenth month | Li Dong — Beginning of Winter | Around November 7 |
| Zi (子) | Eleventh month | Da Xue — Major Snow | Around December 7 |
| Chou (丑) | Twelfth month | Xiao Han — Minor Cold | Around January 6 |
These Gregorian dates can vary by a day or two each year. Consult that year's calendar for the exact hour and minute.
An example
In 2024, Li Chun occurred on February 4 at 16:27 Beijing time. Consider two people born just two days apart.
| Birth date | Lunar calendar date | BaZi Year Pillar | BaZi Month Pillar |
|---|---|---|---|
| February 3, 2024 | Gui-Mao year, twelfth lunar month, day 24 | Gui-Mao (癸卯), Rabbit | Yi-Chou (乙丑) |
| February 5, 2024 | Gui-Mao year, twelfth lunar month, day 26 | Jia-Chen (甲辰), Dragon | Bing-Yin (丙寅) |
Both births occurred in the twelfth lunar month; Lunar New Year was not until February 10. But the second birth followed Li Chun, placing it in the first BaZi month of the Dragon year. Both the Year and Month Pillars changed.
Why not use lunar months?
Traditional elemental strength is closely tied to the seasons: Yin and Mao months mark spring and Wood; Si and Wu mark summer and Fire; Shen and You mark autumn and Metal; Hai and Zi mark winter and Water. Solar terms track the Sun's position and therefore the seasons.
Lunar months follow the Moon's phases. Their alignment with the seasons varies from year to year, and leap months are added. Using their first days as Month Pillar boundaries would not preserve the same seasonal alignment.
What to check near a solar-term boundary
- If a birth falls within a day or two of a transition, check its exact time for that year, down to the minute.
- A solar-term transition is one fixed instant, often published in Beijing time. Compare the birth time in that same time zone; convert an overseas birth before deciding which came first.
- Li Chun is especially important because the Year and Month Pillars change together. Check both.
This page introduces traditional culture knowledge for reference only; it makes no predictions or guarantees about fate, health, relationships or wealth.