Leap month attribution
The lunar calendar inserts a leap month roughly every two or three years. For people born in one, which month should Zi Wei Dou Shu use? The classical schools disagree — this is the second gate of chart correctness.
1. Where the dispute lies
Zi Wei Dou Shu places stars using the lunar month as a key parameter (the Ming Palace and the Five Element Bureau both depend on it). A leap month is “an extra month”; the classics do not record a uniform rule for it, and two mainstream conventions formed:
| Convention | Rule | Status |
|---|---|---|
| Whole month to the current month | The whole leap month is charted as the current (previous normal) month | Mainstream; our default |
| Split at the 15th | Before the 15th → current month; on/after → next month | Used by some schools |
2. Our approach: both schools implemented, mainstream by default
Both conventions are fully implemented and switchable on the chart page — people born in a leap month can directly see how the Ming Palace differs under each, instead of us silently choosing for you. The default is the mainstream whole-month rule.
The calendar spans 1900–2100 — two hundred years, with every lunar leap month covered.
3. The engineering leap-month trap — fixed
Leap months are one of the most error-prone edges of any chart engine. A well-known historical issue of the engine we use — misplacement of the Santai and Bazuo stars in leap months — was fixed in v2.4.7, and the v2.5.8 we run includes that fix. Leap-month edges are also covered by our 560-item full-field benchmark (see Verification data).