Chart calculation rules

Other trust pages: About · Sources · Corrections · Disclaimer · Methodology

The methodology page carries the full derivations and reconciliations; this page lists every decision point in casting a chart — which convention applies where, which school this site follows, and why. After this page you should be able to trace any pillar back to a rule.

Every decision point

DecisionThis site’s ruleDivergence / noteCard
Year pillarSwitches at the lichun instant (sun at 315°). A minute-level table of 201 entries (1900–2100); e.g. the 2024 instant is Feb 4, 16:27Not New Year’s Day, not lunar new yearR1
Month pillarSwitches at the exact term instant, even mid-dayNot the lunar month startR2, R4b
Day pillarRolls the day at 23:00 (late-zi convention, the mainstream default)The other school rolls at midnight; this site uses the mainstream and says soR3
Hour pillarTwo-hour blocks, aligned to true solar time v1 (4 minutes per degree of longitude)Overseas births need a longitude or UTC offset or block edges slipR4
DSTChina’s 1986–1991 DST is handledInvisible if absent — it matters for six summersR5
Unknown hourFalls back to three pillars and says so, with three element-count readingsPretending to an answer would be the errorR6–R7
Ten godsTwo-step mapping (element → relation), always relative to the true day masterThe ten gods map one-to-one onto their order — checkable term by termR4c, R29
Luck pillarsForward for yang-year men and yin-year women; starting age from the distance to the next term: 3 days = 1 year, 1 day = 4 months, 1 shichen = 10 daysDirection reversed flips the whole sequence — guarded by a 4,939-assertion suiteR8–R9
ZodiacZodiac switches at lichunThe convention this site is asked about mostR30
Kua numberThe kua number switches at lichun too, same boundary as the year pillarBoth century formulas are congruent to one uniform formula mod 9 — the tables interlockR36

A worked chart

1985-07-04 12:00, Beijing time (UTC+8). Every cell is engine-computed — paste it into the home calculator to verify:

PillarStem-branchTen god (vs day master)Na yinHidden stems
Year乙丑 Yi ChouRob Wealth海中金己、癸、辛
Month壬午 Ren WuIndirect Resource杨柳木丁、己
Day甲辰 Jia ChenDay master覆灯火戊、乙、癸
Hour庚午 Geng WuSeven Killings路旁土丁、己

Where schools disagree

Frequently asked questions

Why does my zodiac animal differ from other sites?
Most likely you were born near a switch point: for people born around lichun (Feb 3–5), the lichun convention and the lunar-new-year convention give different animals. This site uses lichun (sun at 315°, minute-level table), consistent with the year pillar.
I was born at 23:00 — which day is my pillar?
This site follows the mainstream late-zi convention: from 23:00 the day pillar rolls to the next day. It is a published convention (not the only possible one), applied consistently to the month pillar and luck pillars so the whole chart agrees.
How are overseas birth times handled?
Enter a birth place (longitude and offset are resolved) or provide longitude and UTC offset under advanced options; hour-block edges are aligned to true solar time v1. China’s 1986–1991 DST is handled automatically.
What if I do not know my birth hour?
The chart falls back to three pillars: year, month and day stay; the hour is marked unavailable; element counts are given under three declared readings. The site never pretends a fourth pillar exists.

Reference index

Every enumerable component of ba zi has its own page here. Each page is computed by the same engine and can be checked item by item — none of it is a personality table.