乙亥 Day Pillar — Yi Yin Wood Day Master (hai Pig)
The yi hai (乙亥) day pillar means you are a Yi Yin Wood day master sitting on the hai (Pig, 水) branch. Its nayin is Fire on the Hilltop (山头火). Below: what the stem says, what the branch adds, and how the pair interacts.
The 乙亥 day pillar at a glance
| Position in the cycle | No. 12 of the 60 day pillars |
|---|---|
| Day master (heavenly stem) | 乙 — Yi Yin Wood (Wood) |
| Day branch (earthly branch) | 亥 — hai, the Pig (Water) |
| Hidden stems | 壬 (Ren Water), 甲 (Jia Wood) |
| Nayin | Fire on the Hilltop (山头火) |
| Stem–branch relation | the branch feeds the stem |
What the day pillar means in BaZi
In the Four Pillars of Destiny (BaZi), the day pillar is the pillar of the self: its heavenly stem is your day master, the element that represents you, and its earthly branch is the ground you stand on, closest to your inner life and (traditionally) your marriage palace. All other pillars are read in relation to the day stem. That is why the 60 day pillars are the most-asked-about combinations in Chinese astrology: one glance at this one character pair already sketches a person.
The day master: Yi Yin Wood (乙)
Yi is the vine and the flowering stem: softer in form, tougher in survival. This day master adapts to whatever structure surrounds it, wins by flexibility and timing rather than force, and holds on where harder characters snap.
The day branch: hai Pig (亥, 水)
Hai is the Pig: deep water with wood growing inside. As a day branch it adds generosity, easy-going depth, and hidden ambitions.
The hai branch hides Ren Water, Jia Wood in its depths, which the full chart reads as secondary characters underneath the surface.
How the stem and branch interact
The branch feeds the stem in the generating cycle, so this day master draws quiet strength from underneath: reserves it can tap when pressed.
What it is like when Yi Yin Wood sits on hai
This pairing sits on its own resource: the branch generates the stem in the producing cycle, so the ground under the day master keeps feeding it. Classical reading treats reserved strength of this kind as quiet staying power — setbacks usually cost less than they look, and recovery is faster than the person tends to admit. The traditional caution is the mirror image: when support always arrives from underneath, initiating can feel optional, and a person with this pillar may wait longer than they should before acting. Practitioners read it as better built for enduring than for launching.
Taken together, the 乙亥 day pillar sketches a Yi Yin Wood day master whosehai ground feeds it. Classical commentary always adds the same caveat: a day pillar is one character pair in a four-pillar chart, and the month branch — the season your chart was born into — can strengthen or exhaust any stem. Treat everything on this page as the first paragraph of the reading, never the whole of it.
The nayin of 乙亥: Fire on the Hilltop
In the classical sexagenary verse system (nayin), the 乙亥 pillar is Fire on the Hilltop (山头火). The nayin system assigns one of thirty poetic images to the sixty pillars two at a time: 乙亥 shares its image with 乙酉, its neighbour in the cycle. The image belongs to a different element than the stem itself — nayin is a second, older layer of description laid over the pair.
Traditional commentators used the nayin image to summarise a pillar's texture rather than to compute with it. Fire on the Hilltop is read as exactly that — an image of how the Yi Yin Wood / hai combination feels from the outside. Treat it as flavour, not as a separate engine.
乙亥 elsewhere in the chart
The 乙亥 pairing does not only appear as a day pillar. The same stem-branch pair can occupy the year, month or hour pillar, and classical reading shifts its role with the seat: in the year pillar it describes the background — family atmosphere, early environment, the generational weather; in the month pillar, the season that sets the whole chart's balance, alongside the world of siblings, peers and career structure; in the hour pillar, the late chapters, children and private ambitions. When the same pair shows up in two seats, commentators read a doubling of its character — the themes above get a larger stage. If 乙亥 appears in your chart at all, it is worth knowing this page even if it is not your day pillar.
Find your own day pillar
Your day pillar comes from your birth date (the day changes at midnight, and in classical practice the hour matters for the other three pillars). The free BaZi calculator on this site computes your four pillars, hidden stems and ten gods locally in your browser, no sign-up needed. If your result shows 乙亥 on the day pillar, this page is you.
Frequently asked questions about the 乙亥 day pillar
It means your day master is Yi Yin Wood (乙) and it sits on the hai(Pig) branch. The stem describes your core character; the branch describes the ground under it. Their combination (the branch feeds the stem) is the first sketch of how you carry that character.
It is the anchor, not the whole picture. Practitioners weight the day stem most heavily because every other element is judged from its position, but the month branch (your season) and the luck pillars tell you when that character gets its chances. Read all four pillars together.
Check the heavenly stem of your birth day. A free chart calculationtakes seconds; if the day pillar reads 乙亥, the description on this page applies to you. Your stem repeats every ten days, but the 乙亥 pairing comes around once in the full sixty-day cycle.
Two answers, both classical. By the stem: the day master is Yi Yin Wood, a Wood day master, and that is the element practitioners count first. By the branch: the hai below it is Water. In the nayin verse system the pair as a whole counts as Fire on the Hilltop (山头火).
Once every sixty days. Days run in an unbroken sexagenary cycle — ten stems cycling against twelve branches, same-polarity pairs only — so each of the 60 pairings, 乙亥 included, falls on one day per full cycle. That fixed rhythm is why a birth date alone pins the day pillar down exactly.
Fire on the Hilltop (山头火). The nayin system assigns thirty images to the sixty pillars two at a time, so 乙亥 shares the image with 乙酉, the neighbouring pillar in the cycle. It is read as a poetic summary of the pair's texture, not as a separate calculation.