By name: calculate-bazi description: Calculate Four Pillars (四柱) from birth date/time using lunar calendar conversion. Foundation skill for all BaZi analysis.
Calculate BaZi
This skill calculates the Four Pillars (四柱 Sì Zhù) - the foundation of all BaZi fortune analysis. It converts birth date/time to the traditional Chinese lunar calendar and determines the Heavenly Stems (天干) and Earthly Branches (地支) for each pillar.
When to Use This Skill
- New consultation: Starting any BaZi analysis
- Verification: Double-checking existing calculations
- Batch processing: Calculating charts for multiple people
- Compatibility analysis: Preparing charts for relationship matching
What This Skill Does
- Lunar Calendar Conversion: Converts Gregorian date to Chinese lunar calendar
- Four Pillars Calculation: Determines Year, Month, Day, Hour pillars
- Hidden Stems Extraction: Identifies Hidden Stems (地支藏干) in each Earthly Branch
- Day Master Identification: Identifies the Heavenly Stem of Day Pillar (日主)
- Luck Cycle Setup: Calculates 10-year luck cycle starting points (大运)
- Data Validation: Verifies calculation accuracy and completeness
Required Information
Essential
- Birth Date: Year, Month, Day (Gregorian or Chinese)
- Birth Time: Hour and minute (as accurate as possible)
- Gender: Male (阳) or Female (阴) - affects luck cycle direction
Recommended
- Birth Location: For timezone and local solar time adjustment
- Birth Country: For historical timezone rules
- Name: For personalized reporting
How to Use
Basic Calculation
Calculate BaZi for:
- Born: 1990年1月15日 18:30
- Gender: Male
- Location: Beijing, China
With English Date
Calculate Four Pillars for someone born:
- Date: January 15, 1990
- Time: 6:30 PM
- Gender: Female
- Location: San Francisco, USA
Multiple People
Calculate BaZi for compatibility analysis:
Person A:
- Born: 1988年3月22日 14:00
- Gender: Male
- Location: Shanghai
Person B:
- Born: 1990年7月8日 09:15
- Gender: Female
- Location: Beijing
Output Format
Four Pillars Display
八字命盘 (BaZi Chart)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
姓名：[Name]
性别：[Gender]
公历：1990年1月15日 18:30
农历：己巳年 腊月十九 酉时
┌─────┬─────┬─────┬─────┐
│ 年柱 │ 月柱 │ 日柱 │ 时柱 │
│Year │Month│ Day │Hour │
├─────┼─────┼─────┼─────┤
│ 己 │ 丁 │ 甲 │ 癸 │
│ 土 │ 火 │ 木 │ 水 │
├─────┼─────┼─────┼─────┤
│ 巳 │ 丑 │ 子 │ 酉 │
│ 火 │ 土 │ 水 │ 金 │
└─────┴─────┴─────┴─────┘
日主：甲木 (Day Master: Wood)
命格：[Pattern classification]
地支藏干 (Hidden Stems):
- 巳 (Fire): 庚金, 丙火, 戊土
- 丑 (Earth): 己土, 癸水, 辛金
- 子 (Water): 癸水
- 酉 (Metal): 辛金
五行统计 (Five Elements Count):
木 (Wood): 1
火 (Fire): 2
土 (Earth): 3
金 (Metal): 2
水 (Water): 3
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
JSON Data Structure
{
"personalInfo": {
"name": "User Name",
"gender": "male",
"birthDate": {
"gregorian": "1990-01-15T18:30:00+08:00",
"lunar": "己巳年腊月十九酉时",
"year": 1990,
"month": 1,
"day": 15,
"hour": 18,
"minute": 30,
"timezone": "+08:00"
},
"location": "Beijing, China"
},
"fourPillars": {
"year": {
"stem": "己",
"branch": "巳",
"element": {
"stem": "土",
"branch": "火"
},
"hiddenStems": ["庚", "丙", "戊"]
},
"month": {
"stem": "丁",
"branch": "丑",
"element": {
"stem": "火",
"branch": "土"
},
"hiddenStems": ["己", "癸", "辛"]
},
"day": {
"stem": "甲",
"branch": "子",
"element": {
"stem": "木",
"branch": "水"
},
"hiddenStems": ["癸"]
},
"hour": {
"stem": "癸",
"branch": "酉",
"element": {
"stem": "水",
"branch": "金"
},
"hiddenStems": ["辛"]
}
},
"dayMaster": {
"stem": "甲",
"element": "木",
"yinYang": "阳"
},
"elementsBalance": {
"wood": 1,
"fire": 2,
"earth": 3,
"metal": 2,
"water": 3
},
"luckCycle": {
"direction": "forward",
"startAge": 3,
"cycles": [...]
}
}
Technical Details
Calculation Steps
Timezone Adjustment
- Convert to local solar time
- Account for daylight saving (if applicable)
- Adjust for geographic longitude
Lunar Calendar Conversion
- Map Gregorian date to Chinese lunar date
- Identify solar term (节气) for month pillar
- Determine correct year boundary (立春 vs. 正月初一)
Pillar Derivation
- Year Pillar: Based on year of 立春 (Start of Spring)
- Month Pillar: Based on solar term of birth month
- Day Pillar: Use万年历 (perpetual calendar) lookup
- Hour Pillar: Divide day into 12 two-hour periods
Hidden Stems Extraction
- Each Earthly Branch contains 1-3 Hidden Stems
- Primary, middle, and residual stems have different influence strengths
Luck Cycle Calculation
- Male Yang year or Female Yin year: Forward direction
- Male Yin year or Female Yang year: Backward direction
- Calculate starting age based on birth proximity to solar term
Edge Cases
Midnight Births (23:00-01:00)
- 23:00-24:00: Previous day's Hour Pillar (子时)
- 00:00-01:00: Current day's Hour Pillar (子时)
- Always confirm with user which "night" they remember
Near Solar Term Births
- Month pillar changes at solar term, not lunar month
- Verify exact solar term timestamp for boundary dates
Historical Timezone Changes
- Use historical timezone rules for older birth dates
- Pre-1949 China: Use local solar time
- 1949-1986: Single China timezone established
- Post-1986: Modern timezone rules
Leap Months (闰月)
- Lunar calendar occasionally has 13 months
- Use the same solar term rules for month pillar
- Document leap month in lunar date notation
Best Practices
Accuracy Checks
- ✅ Verify birth time with user (exact time, AM/PM, timezone)
- ✅ Confirm location for timezone adjustment
- ✅ Cross-reference with perpetual calendar (万年历)
- ✅ Validate elemental counts add up correctly
- ✅ Check Hidden Stems match standard references
User Communication
- Explain why accurate birth time matters
- Offer to calculate with time range if uncertain
- Mention common time recording issues (hospital clock vs. actual, DST)
- Provide calculation breakdown for transparency
Data Storage
- Save calculation details in
./output/charts/[name]-[date].json - Keep human-readable version in
.mdformat - Include metadata (calculation date, version, method)
- Store source data (raw input) separately
Common Issues & Solutions
Issue: Birth time unknown Solution: Calculate for 12:00 noon (default) and note uncertainty. Offer range analysis.
Issue: Born in different country, different timezone Solution: Use historical timezone database (e.g., IANA TZ). Explicitly state assumptions.
Issue: Conflicting lunar calendar sources Solution: Use authoritative source (中国科学院紫金山天文台). Document methodology.
Issue: Leap month confusion Solution: Always verify with solar term. Leap months don't affect month pillar.
Implementation
Core Library
This skill uses the shared BaZi Core Library located at .claude/lib/bazi_core.py.
Python API:
from lib.bazi_core import BaZiCalculator
calculator = BaZiCalculator()
result = calculator.calculate_bazi(
birth_date="1990-05-15", # Format: YYYY-MM-DD
birth_time="10:00", # Format: HH:MM
location="北京" # Optional, default: 北京
)
# Access results
print(result['four_pillars'])
print(result['day_master'])
print(result['elements_balance'])
Command Line:
# Basic usage
python /bunny-agent/.claude/lib/bazi_core.py 1990-05-15 10:00 北京
# With JSON output
python /bunny-agent/.claude/lib/bazi_core.py 1990-05-15 10:00 北京 --json
Manual Verification
- Cross-check with online 万年历 (perpetual calendar)
- Verify against printed BaZi almanacs
- Use multiple sources for critical consultations
Output Files
After calculation, generates:
./output/charts/[name]-bazi-[YYYYMMDD].json- Complete data./output/charts/[name]-bazi-[YYYYMMDD].md- Readable format./output/charts/[name]-bazi-[YYYYMMDD].txt- Plain text for printing
Next Steps
After calculating BaZi:
- ✅ Verify accuracy with user
- ➡️ day-master-analysis: Analyze core personality
- ➡️ five-elements-balance: Examine elemental distribution
- ➡️ luck-cycle-forecast: Interpret timing and trends
Principle: 差之毫厘，谬以千里 - A tiny error in calculation leads to vastly different conclusions. Accuracy is paramount.