Hour Pillar Calculation in Bazi
Calculate the two-hour branch and use the Five Rats method for the hour stem, with explicit handling for Zi hour, time zones and day boundaries.
Overview
The Hour Pillar combines a two-hour Earthly Branch with a Heavenly Stem derived from the effective Day Stem. Zi covers 23:00–00:59, Chou 01:00–02:59, and the branch sequence continues in two-hour blocks. The Five Rats rule assigns the Zi-hour stem from the Day Stem, then advances one stem per branch. Historical time zone, optional true-solar correction and the selected day-boundary doctrine must be resolved before the final pillar is emitted.
At a glance
- Branch blocks
- Twelve two-hour intervals
- Zi interval
- 23:00–00:59 after selected time normalization
- Hour-Stem input
- Effective Day Stem
- Hour-Stem rule
- Five Rats starts at Zi and advances by branch
- Sensitive settings
- Time zone, solar correction and day rollover
- Boundary
- Recorded uncertainty can produce multiple candidates
First assign the branch from a normalized local or solar time
The twelve branch hours are centered on odd civil hours: Zi crosses midnight, Chou covers 01:00–02:59, Yin covers 03:00–04:59, and the pattern continues.
If true solar time is enabled, the corrected clock is used according to the declared product contract. The uncorrected recorded time should remain in provenance.
- Resolve time zone before the branch.
- Show whether civil or true solar time supplied the branch.
Five Rats derives the Zi-hour stem from the Day Stem
Jia or Ji days start Zi hour with Jia; Yi or Geng with Bing; Bing or Xin with Wu; Ding or Ren with Geng; and Wu or Gui with Ren.
From the Zi-hour start, advance one Heavenly Stem for each successive branch. The branch and stem calculations are connected but auditable separately.
- Use the effective Day Stem.
- Advance one stem per two-hour branch.
Late Zi exposes the interaction between hour and day rules
At 23:00–23:59, the selected day-rollover doctrine can change which Day Stem feeds Five Rats. OpenFate supports explicit modes rather than hiding the disagreement.
A time rounded across 23:00, midnight or a true-solar boundary can therefore change one or more characters. Sensitivity should be shown when input precision is insufficient.
- Keep rollover mode with the saved chart.
- Do not silently round a boundary birth.
The Hour Pillar does not prove children, career or private intentions
Traditional readings may associate the hour position with later life, projects or descendants, but the pillar alone cannot establish those outcomes.
Calculation precision should not be confused with interpretive certainty. High-stakes claims still require real-world evidence and the complete chart.
- No specific life event from the hour alone.
- Separate deterministic symbols from interpretive language.
Sources and editorial basis
- Hong Kong Observatory: Heavenly Stems and Earthly Branches香港天文台天干地支次序提供十二時辰地支與十天干循環所需的基本序列An official modern reference for the canonical stem and branch orders, the sexagenary cycle, and calendrical use.
- 《三命通會》 (Sanming Tonghui)《三命通會》日上起時法：甲己還加甲等五鼠遁規則，先定時支再由日干推時干A historical compilation covering stems and branches, Ten Gods, Nayin, Shen Sha, and multiple classical pattern systems.
- OpenFate Editorial Methodologytests/bazi/test-pillar-invariants.ts 驗證十二時辰、五鼠遁、子時跨日與兩種日界口徑；未知出生時不應假造時柱OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.