Chart conventions
Mingpath's chart conventions: the hour pillar uses true solar time (longitude plus the equation of time); year and month pillars change at the exact solar-term moments; the late Zi hour keeps the same day by default; luck pillars start at three days per year; Ziping school; Zi Wei via iztro.
The same birth time gives different charts under different conventions. Every convention Mingpath uses is written here and worked through on one example, so you can check it against any almanac or another calculator.
Example: male, born 25 January 1999, 23:26 in Shanghai (121.47°E, UTC+8). Every number below is computed by the site's deterministic engine when this page is built.
1. True solar time
Clock time is the time-zone mean (UTC+8 is based on 120°E). Each degree east of that puts the sun 4 minutes earlier; then the equation of time (from the elliptical orbit and axial tilt, between −14 and +16 minutes over the year) is added.
| Clock time | 23:26 |
|---|---|
| Longitude | (121.47 − 120) × 4 min ≈ +5.9 min |
| Equation of time (25 Jan) | -12.3 min |
| Total | -6.4 min |
| True solar time | 1999-01-25 23:19 |
The hour pillar uses true solar time. Pass trueSolar=false to the API to use clock time instead.
2. Year and month pillars change at exact solar-term moments
The year pillar changes at the exact moment of Lichun (Start of Spring), not at Lunar New Year; the month pillar changes at each of the twelve "jie" terms. The example is born before Lichun 1999 (4 February), so the year pillar is still 戊寅 and the month pillar is 乙丑.
3. The Zi hour: two conventions, default keeps the day
| School 1: late Zi moves the day | School 2: late Zi keeps the day (default) | |
|---|---|---|
| Rule | From 23:00 it is the next day | Same day pillar; hour stem from the next day's stem |
| Example | 戊寅 乙丑 戊寅 壬子 | 戊寅 乙丑 丁丑 壬子 |
Only the day pillar differs (戊寅 vs 丁丑) — and the day stem is the Day Master. Pass ziRule=1 for school 1. Life readings for late-Zi births include a section reading the chart under the other convention too.
4. Luck pillars: three days to a year
Luck pillars run from the month pillar, forward for yang-year men and yin-year women (counting to the next jie), backward otherwise. The days from birth to that jie convert at three days per year, one day per four months, one double-hour per ten days. Example: starts 2002-04-14; first luck pillar 丙寅 from 2002 (age 4, East Asian reckoning), ten years each.
5. School: Ziping
The day stem is the self; strength is judged from the month first, then the useful elements. Strength is a published score (season + roots − support/drain) printed in the book. No "blind school" formulas.
6. Zi Wei Dou Shu defaults
Computed with the open-source iztro library from the same true solar time and Zi-hour rule. Leap months split at the 15th; the standard ten-stem transformation table; yearly charts are taken at mid-year. Example: 金四局, Life palace 乙丑 (紫微, 破军), soul star 巨门, body star 天梁.
7. Unknown birth hour
Three pillars only; no Zi Wei chart. Question books still compute windows, and the preview and book say: good times are estimated from three pillars, so less precise.
8. Engines
BaZi: open-source 6tail lunar (MIT), cross-checked against an independent implementation on 406 dates. Zi Wei: iztro (MIT). All deterministic; the AI never calculates. The free chart is computed in your browser.
Cite this page: Mingpath, “Chart conventions”, https://mingpath.app/en/conventions/, updated 2026-11-08.