In BaZi (八字, Four Pillars), a chart has four pillars — year, month, day and hour — and each pillar pairs a heavenly stem above an earthly branch. That is eight characters, hence the name. The stem sitting above the day pillar is the Day Master, and it represents the person the chart is about.
Every other character in the chart is interpreted by its relationship to the Day Master, not on its own terms. The same 庚 Metal is an ally in one chart, a source of pressure in another, and a marker of wealth in a third — the difference is entirely which Day Master is doing the looking. Change the Day Master and the same eight characters mean something completely different.
There are ten heavenly stems, so there are ten Day Masters: the five elements each in a yang and a yin form. The yang form is not a stronger version of the yin one — they behave differently. 甲 Yang Wood grows through an obstacle or stops; 乙 Yin Wood grows around it. Autumn Metal fells the first and prunes the second. Treating the pair as interchangeable is one of the most common mistakes in English-language material on the subject.
The Day Master depends on the exact day you were born, and BaZi days do not begin at midnight or change at calendar month boundaries. Three corrections matter, and getting any of them wrong can change the Day Master itself rather than merely shading the reading.
The BaZi month changes at a solar term (節氣), not on the first of the month. A birth in early February may still belong to the previous BaZi year, because 立春 — the start of spring — usually falls around 4 February. This is why a chart calculated from a Western calendar month is frequently wrong at the boundaries.
Clock time is a political convention; the chart wants the sun's actual position. Birth times are adjusted for the longitude of the birthplace, and for historical daylight saving where it applied. Hong Kong observed DST intermittently between 1941 and 1979, and Singapore ran on UTC+7:30 until 1982 — corrections that move a borderline birth across an hour boundary and occasionally across a day boundary.
The Zi hour (子時) straddles midnight, running from 23:00 to 01:00. Births between 23:00 and midnight fall in the late Zi hour (晚子), which advances the day pillar to the next day. A birth at 23:30 therefore has a different Day Master from one at 22:30 on the same evening. Systems that ignore this are wrong for roughly one birth in twenty-four.
Most people don't, and it matters less than you would expect for this particular question. The day pillar — and therefore your Day Master — is determined by the date, so it remains reliable regardless of birth time, with the single exception of births near 23:00 where the late Zi hour is in play. What you lose without a birth time is the hour pillar, which is a quarter of the chart, and any reading that depends on it.
Every other stem in a chart stands in one of ten relationships to the Day Master. These are the Ten Gods (十神). They describe function, not personality — what a stem does to yours. Which stem produces which relation depends entirely on your own Day Master, and is shown on each of the ten pages above.
| Relation | What it means |
|---|---|
| Friend 比肩 | A peer standing beside you. Self-reliance, allies, and competition for the same resources. |
| Rob Wealth 劫財 | A rival with your own face. Drive and daring, but the classic marker for money leaving through other people. |
| Eating God 食神 | Easy output. Talent that flows without strain — making, cooking, teaching, enjoying. |
| Hurting Officer 傷官 | Sharp output. Brilliance and originality that cuts; the stem most associated with saying the true thing badly. |
| Direct Wealth 正財 | Earned wealth. Steady return that is proportional to effort — salary, contracts, the reliable kind. |
| Indirect Wealth 偏財 | Opportunity wealth. Windfalls, side ventures, money that arrives through people and timing. |
| Direct Officer 正官 | Legitimate authority. Structure, office, rules you accept — status earned by conforming well. |
| Seven Killings 七殺 | Raw pressure. Challenge, rivalry, and force; it builds you or grinds you depending on chart strength. |
| Direct Resource 正印 | Orthodox support. Mentors, study, credentials, and the instinct to be protected. |
| Indirect Resource 偏印 | Unorthodox support. Intuition and niche expertise; insight bought at the cost of conventional backing. |
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