Solar Terms and BaZi Months

The month pillar is the most important pillar for judging strength, because its branch — the month command (月令) — tells you which element is in season. Yet it is also the pillar most often misunderstood, because BaZi months are not lunar months. They are defined by the solar terms.

Twenty-four terms, twelve months

The sun's apparent path through the year is divided into twenty-four solar terms (二十四节气), each 15° of ecliptic longitude apart. They alternate between two kinds:

• Jie (节) terms — 立春, 惊蛰, 清明, 立夏, 芒种, 小暑, 立秋, 白露, 寒露, 立冬, 大雪, 小寒 — begin the twelve BaZi months.
• Zhong qi (中气) terms — 雨水, 春分, 谷雨, 小满, 夏至, 大暑, 处暑, 秋分, 霜降, 小雪, 冬至, 大寒 — fall in the middle of each month.

Only the jie terms matter for the month pillar. A birth one minute before 惊蛰 is in the 寅 month; one minute after, in the 卯 month.

Here are the jie instants for 2026, in Beijing time:

Month branches are fixed

Every year, the 寅 month starts at 立春, 卯 at 惊蛰, 辰 at 清明, and so on to 丑 at 小寒. The branch of a BaZi month is therefore always the same for a given season: a birth in late March is always in a 卯 month, a birth in mid-August always in a 申 month (after 立秋).

Month stems come from the year

The month stem cycles through the ten stems over five years. The rule, known as the "five tigers" (五虎遁), gives the stem of the 寅 month from the year stem:

The following months continue in order: if 寅 is 丙寅, then 卯 is 丁卯, 辰 is 戊辰, and so on. This is why a wrong year pillar (for example a January birth assigned to the new year) also gives a wrong month stem.

Lunar months are different

Lunar months begin at each new moon and are numbered from the lunar New Year. They drift against the solar terms by up to a month, and a leap month is inserted about every three years. A lunar date such as "the third day of the second month" can fall in either the 寅 or the 卯 BaZi month depending on the year. BaZi never uses the lunar month number.

Births on a solar-term day

On the day of a jie term, the month pillar depends on the exact birth time relative to the term's instant. The calculator compares the two to the minute, after converting your birth time to the correct time zone. If your birth time is uncertain by more than the distance to the term, the month pillar is uncertain too — the result will flag it.

The solar-term instant also sets the starting age of luck pillars: the time between birth and the neighbouring jie term, converted at three days per year. See luck pillars.

The month command

Once the month branch is known, it sets the season:

• 寅卯 (and early 辰): spring — wood is prosperous.
• 巳午 (and early 未): summer — fire is prosperous.
• 申酉 (and early 戌): autumn — metal is prosperous.
• 亥子 (and early 丑): winter — water is prosperous.
• 辰戌丑未: the storage months, in which earth is prosperous.

This is the first factor in judging Day Master strength.

Jie and qi: the two kinds of solar term

The twenty-four terms alternate between jie (节, "sections") and qi (气, "breaths" or mid-terms). Only the twelve jie start BaZi months: 立春, 惊蛰, 清明, 立夏, 芒种, 小暑, 立秋, 白露, 寒露, 立冬, 大雪, 小寒. The twelve qi — 雨水, 春分, 谷雨, 小满, 夏至, 大暑, 处暑, 秋分, 霜降, 小雪, 冬至, 大寒 — fall in the middle of each month. They matter in other systems (for example, the winter and summer solstices switch yin and yang dun in Qi Men Dun Jia), but they do not change the BaZi month.

How terms are computed

Each term is the moment the sun reaches a multiple of 15° of ecliptic longitude: 0° for 春分, 15° for 清明, 315° for 立春, and so on. Because Earth's orbit is elliptical, the sun moves faster in early January and slower in early July, so months near the northern winter are slightly shorter (about 29.5 days) than those near summer (about 31.5 days). This calculator computes each term astronomically to the minute rather than using fixed dates.

The month stem rule

The month stem follows from the year stem by a fixed rule, often memorised as 甲己之年丙作首:

The remaining months follow in order. In a 丙午 year such as 2026, the months run 庚寅, 辛卯, 壬辰, 癸巳, 甲午, 乙未, 丙申, 丁酉, 戊戌, 己亥, 庚子, 辛丑. You can check any month with the Chinese calendar converter.

Solar terms and luck pillars

Solar terms also set the luck pillar starting age. The calculator counts the time from birth to the next jie (for forward luck) or back to the previous jie (for backward luck), and in the traditional ratio three days correspond to one year. A birth one day after a jie with backward luck therefore starts its first luck pillar at about four months of age; a birth two weeks before the next jie with forward luck starts at about five years. The luck pillar calculator shows the computed starting age.

Solar terms in daily life

Solar terms predate BaZi and remain part of the agricultural calendar. The Chinese almanac uses the same jie to define its months, so the day officers and many yi/ji indications change at the same boundaries as BaZi months.

Checking your own month pillar

1. Compute your chart with the BaZi calculator.
2. Look up the jie before and after your birth in the converter.
3. If your birth is within a day of a jie, double-check the time zone and recorded time; the month pillar — and with it the season, which is the most important factor for strength — depends on it.

A worked example near a boundary

Consider a birth on 5 March 2026. The jie 惊蛰, which starts the 卯 month, fell on 5 March 2026 at about 21:59 Beijing time. A birth at 10:00 that morning is still in the 寅 month (庚寅); a birth at 22:30 that evening is in the 卯 month (辛卯). The two charts share the year and day pillars, but the month pillar differs — and so does the season's weighting, since 寅 is early spring with 丙 and 戊 hidden, while 卯 is pure wood at its peak. For a metal or earth Day Master this can change the strength judgement. The Chinese calendar converter shows the exact instant of each term, so you can check how close a birth is.

Quick reference: the twelve jie and their months

Key points

• BaZi months are solar, not lunar. They begin at the twelve jie terms, starting with 立春 for the 寅 month.
• The twelve qi mid-terms, such as 春分 and 冬至, fall inside months and do not change the month pillar.
• Terms are astronomical instants at multiples of 15° of solar longitude, so each has an exact minute, which differs from year to year.
• The month stem follows from the year stem by the 甲己之年丙作首 rule. In 2026 (丙午) the months run from 庚寅 to 辛丑.
• The month branch sets the season. It is the largest single factor in judging Day Master strength.
• The time from birth to the nearest jie sets the luck-pillar starting age, using the ratio of three days to one year.
• Births within a day of a jie need a careful check of time zone, recorded time and daylight saving.
• The Chinese almanac uses the same jie boundaries, so its day officers and many yi/ji indications change with the BaZi month.

If you remember only one thing from this article, remember that the lunar date printed on a calendar is not used to set the BaZi month. Always check the solar term instead.

Key terms in this article

Solar Terms · 二十四节气

The twenty-four solar terms divide the sun's path into 15° steps. The twelve 节 (jie) terms such as 立春 and 惊蛰 begin BaZi months; the twelve 中气 terms such as 雨水 mark mid-months. Each term has a precise astronomical moment, not just a date.

Month Pillar · 月柱

The month pillar follows the twelve 节 (jie) solar terms: the 寅 month begins at 立春, 卯 at 惊蛰 and so on. Its branch, the month command (月令), is the single strongest factor in judging seasonal strength. Its stem is derived from the year stem by the "five tigers" rule.

Seasonal Strength · 旺相休囚死

Seasonal strength rates each element by the month: the element of the season is prosperous (旺), the one it generates is strengthening (相), the one that generated it rests (休), the one controlling it is confined (囚) and the one it controls is dead (死). Earth is strongest in the four storage months.

Start of Spring (Li Chun) · 立春

立春, when the sun reaches 315° ecliptic longitude around 4 February, begins the BaZi year and the 寅 month. Someone born on 1 February belongs to the previous BaZi year even if Chinese New Year has passed — or not passed.

Common questions

Why does my month differ from another app? Usually one of them uses dates instead of instants, or a different time zone.

Do zhong qi terms matter? Not for the month pillar. Some advanced techniques use them, and the almanac lists all twenty-four.

Is 小寒 the last month of the year? Yes: the 丑 month runs from 小寒 to 立春, so it belongs to the previous BaZi year.