Calculation Methodology
We calculate first and explain second. Every chart carries a rule-set ID and versions. These defaults are choices we made; they are not the only valid answers across all traditions.
BaZi defaults: bazi.zi23.v1
| Setting | Default |
|---|---|
| Time mode / 时间模式 | True solar time (switchable to local clock) |
| Year boundary / 年界 | Exact 立春 instant |
| Month boundary / 月界 | 12 jie solar-term instants |
| Day boundary / 日界 | 23:00 on the chart clock |
| Hour stem / 时干 | From the effective day stem (after 23:00 rule) |
| Luck direction / 大运顺逆 | Year-stem polarity + traditional gender option |
| Luck start / 起运 | Time to previous/next jie, 3 days = 1 year, minute-level |
| Invalid/repeated clock time / 无效或重复时间 | Never silently fixed: ask, or keep candidates |
Time: three different quantities
We keep apart the clock time on the birth record, the true UTC instant, and the rule-specific chart clock. Clock time is resolved to UTC with the birth city’s IANA time zone (rules for that year). Year and month pillars compare the UTC instant with solar-term instants; day and hour pillars use the chart clock. True solar time never changes the birth instant — it is another representation of it: UTC + longitude × 4 min + equation of time.
Daylight saving
A repeated clock time (fall-back) shows both offsets for you to choose; a skipped time (spring-forward) asks you to check the record. Experts may override the offset; the value and reason are saved with the chart. Time-zone history before 1970 may be incomplete in some regions.
Uncertain birth times
For unknown or ranged times we enumerate the boundaries inside the range that would change the chart and label the result complete, partial or ambiguous — never an uncalibrated “accuracy %”.
Other tools
- ziwei.iztro-default.v1 — built on the open-source iztro library with per-chart configuration.
- liuyao.najia-jingfang.v1 — Jing Fang eight palaces, Na Jia, shi/ying, six relatives, six spirits, void, hidden spirits.
- meihua.xiantian.v1 — Xian Tian numbers; number and time casting.
- qimen.hour-rotating-chai-bu.v1 — hour chart, rotating plate, Chai Bu.
- almanac.lunar-typescript.v1 — almanac entries from fixed tables.
Data sources and range
Calendar and solar terms use the open-source lunar-typescript library (MIT); supported years 1901–2100. City data comes from GeoNames cities15000 (about 34,000 places with population ≥15,000, with IANA time zones), licensed CC BY 4.0 and provided as is without guarantee of completeness; you can enter a time zone and coordinates manually if a place is missing.
AI explanations and limits
AI runs only when you ask, may only cite chart facts, and never creates or changes the chart. These are cultural traditions; we do not claim scientific validation and give no medical, lifespan, investment or fated-marriage conclusions.