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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

1. Lunar Calendar Conversion: Converts Gregorian date to Chinese lunar calendar
2. Four Pillars Calculation: Determines Year, Month, Day, Hour pillars
3. Hidden Stems Extraction: Identifies Hidden Stems (地支藏干) in each Earthly Branch
4. Day Master Identification: Identifies the Heavenly Stem of Day Pillar (日主)
5. Luck Cycle Setup: Calculates 10-year luck cycle starting points (大运)
6. 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

1. Timezone Adjustment

   • Convert to local solar time
   • Account for daylight saving (if applicable)
   • Adjust for geographic longitude

2. 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)

3. 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

4. Hidden Stems Extraction

   • Each Earthly Branch contains 1-3 Hidden Stems
   • Primary, middle, and residual stems have different influence strengths

5. 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 .md format
• 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:

1. ✅ Verify accuracy with user
2. ➡️ day-master-analysis: Analyze core personality
3. ➡️ five-elements-balance: Examine elemental distribution
4. ➡️ luck-cycle-forecast: Interpret timing and trends

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Principle: 差之毫厘，谬以千里 - A tiny error in calculation leads to vastly different conclusions. Accuracy is paramount.