When the birth year carries a 庚 (Gēng) heavenly stem, the stems of all twelve months are set before you check the calendar. This is the bazi month stem table for geng year charts, derived from the Five Tigers rule (五虎遁 wǔhǔdùn): a 庚 year opens its first month on 戊 (Wù), and each following month advances one stem. The full year is below.
The 12 month pillars for a Geng 庚 year
Each month begins at a major solar term (節 jié), not on a calendar date. Find your birth branch and read across.
| Month | Branch | Starts at (solar term) | Month pillar |
|---|---|---|---|
| 1st | Tiger 寅 Yín | Li Chun 立春 (~4 Feb) | 戊寅 Wù Yín |
| 2nd | Rabbit 卯 Mǎo | Jing Zhe 惊蛰 (~6 Mar) | 己卯 Jǐ Mǎo |
| 3rd | Dragon 辰 Chén | Qing Ming 清明 (~5 Apr) | 庚辰 Gēng Chén |
| 4th | Snake 巳 Sì | Li Xia 立夏 (~5 May) | 辛巳 Xīn Sì |
| 5th | Horse 午 Wǔ | Mang Zhong 芒种 (~6 Jun) | 壬午 Rén Wǔ |
| 6th | Goat 未 Wèi | Xiao Shu 小暑 (~7 Jul) | 癸未 Guǐ Wèi |
| 7th | Monkey 申 Shēn | Li Qiu 立秋 (~7 Aug) | 甲申 Jiǎ Shēn |
| 8th | Rooster 酉 Yǒu | Bai Lu 白露 (~7 Sep) | 乙酉 Yǐ Yǒu |
| 9th | Dog 戌 Xū | Han Lu 寒露 (~8 Oct) | 丙戌 Bǐng Xū |
| 10th | Pig 亥 Hài | Li Dong 立冬 (~7 Nov) | 丁亥 Dīng Hài |
| 11th | Rat 子 Zǐ | Da Xue 大雪 (~7 Dec) | 戊子 Wù Zǐ |
| 12th | Ox 丑 Chǒu | Xiao Han 小寒 (~5 Jan) | 己丑 Jǐ Chǒu |
A 庚 year opens on 戊 earth and reaches its own stem 庚 in the third month, the Dragon. That 庚辰, metal on the reservoir of spring earth, marks the Gēng column — the same layout a 乙 year uses.
A worked example
Consider a birth in the Rat month (子 Zǐ) of a 庚 year. The eleventh row gives 戊子 (Wù Zǐ) — a 戊 earth stem over a 子 water branch, earth trying to hold back deep-winter water. The Rat month opens at Da Xue (大雪 dàxuě) around 7 December, so a birth on 5 December of that year is still in the Pig month and reads 丁亥 (Dīng Hài) instead. The pillar swings on which side of Da Xue the birth falls, so confirm the solar term before you commit to the row. The Rat month page then details what that branch’s pure, cold Water does to every Day Master.
Which years use this table
Calendar years ending in 0 carry the 庚 stem: 1990, 2000, 2010, 2020. The standing correction is the Li Chun boundary — the Ba Zi year opens at the solar term around 4 February, so a January 2000 birth, for instance, still belongs to the 1999 己 year and reads from the Ji-year column, usually its 丁丑 Ox month. Chinese New Year, whether it falls in January or February, plays no part in the month pillar at all.
How the rule generates the rows
The Five Tigers mechanic in one line: first-month (寅) stem index = (year-stem-index mod 5) × 2 + 2; each later month adds 1, mod 10. Year stems pair: 甲/己, 乙/庚, 丙/辛, 丁/壬, 戊/癸 share columns. Numbering the stems 甲 0 to 癸 9, 庚 is 6; 6 mod 5 is 1, and (1 × 2) + 2 = 4, the stem 戊 — so the Tiger month opens on 戊寅, exactly as it does for a 乙 year (index 1). Eleven single steps carry the column to its 己丑 close.
What the month pillar governs
The month pillar seats the month palace, which a reading treats as the home of career climate and the parental relationship. It carries more structural weight than any other pillar because the month branch holds the ruling element of the season, and the season is the strongest single factor in the chart’s temperature. That is why the month branch dominates the assessment of a strong or weak Day Master — the season either feeds the Day Master or wears it down. In a 庚 year the month stems open on earth and move through metal and water, shaping how the season’s support lands on the Day Master.
The gate is seasonal: spring 寅卯辰, summer 巳午未, autumn 申酉戌, winter 亥子丑, each grading the Day Master through the five states (旺相休囚死 wàng xiàng xiū qiú sǐ). In the 戊子 example above, a Geng Metal Day Master stands in winter at the Resting grade, its strength draining into the season’s Water — the position unpacked in Geng Metal born in winter. The same Day Master under this table’s 乙酉 Rooster month would instead hold autumn’s Prosperous grade.
Reading it in context
Read the month stem as the first line, not the final word; it interacts with the branch’s hidden stems and the surrounding pillars. Because the Five Tigers rule pairs 庚 with 乙 (Yǐ), the month table for Yi 乙 years is identical to this one and serves as a cross-check. The master month stem table gathers all five columns, and the hour stem table extends the same five-fold logic to the hour pillar.
Geng-year month stem FAQ
Where does the year’s own stem appear?
In the third month: 庚辰, the Dragon. It is the earliest self-appearance of any column except the Ren year’s, and it puts yang Metal on the damp spring Earth that classical texts treat as fertile ground for it — a memorable check that you are on the right table.
I was born in early January 1990. Which column applies?
The previous one twice over: January 1990 sits before Li Chun 1990, so the Ba Zi year is still 己 and the month is that column’s 丁丑 Ox month (or its 丙子 Rat month before Xiao Han around 5 January). This table only takes over from the Li Chun moment.
Do 庚 years and 乙 years produce identical charts?
Only the month-stem column is identical. The year pillar itself differs — different stem, different branch, different animal — and with it the whole chart. Sharing a table means sharing month stems, nothing more.
Verify your own Geng-year month pillar against the true solar-term boundary — plot your full chart free with the Butcher Boy calculator and compare it to the table above.