Compass AI — Bazi (八字) Calculation & Lite Interpretation

This skill gives you the complete reference data and step-by-step algorithms needed to calculate a Chinese Bazi (Four Pillars of Destiny) chart from a person's birth date, time, and location, and to produce a basic personality and fortune interpretation.

⚠️ NO EXTERNAL TOOLS OR LIBRARIES NEEDED. Every calculation in this skill — year pillar, month pillar, day pillar, hour pillar, Ten Gods, Five Elements, Major Fortune Cycles — is performed by you, the AI, using only arithmetic and the lookup tables below. Do NOT attempt to call any tool, install any library, or search the web. Just reason through the steps.

For full AI-powered streaming analysis, life K-line charts, two-person compatibility, daily fortune sticks, and interactive fortune-telling chat, visit Compass AI.

When to Use This Skill

Use this skill when the user:

• Provides a birth date, birth time, and birth city/location and asks for a Bazi (八字) reading
• Asks about their Four Pillars, Day Master, Five Elements balance, Ten Gods, or Major Fortune cycles
• Wants to know their favorable/unfavorable elements (喜用神/忌神)
• Asks about personality traits or career tendencies based on Chinese astrology

Important UX rules:

• Only ask the user for: birth date (年月日), birth time (时辰), gender, and birth city name. Never ask for longitude/latitude — look it up from the City Coordinates table below.
• If the city is not in the table, estimate from the nearest listed city or provincial capital.
• Collect all info in as few turns as possible. Ideally one message: "请告诉我您的出生年月日、时辰、性别和出生城市".

Core Concepts (Quick Reference)

Heavenly Stems (天干) and Their Five Elements

Earthly Branches (地支) and Their Five Elements

Five Elements Generating & Controlling Cycles (五行生克)

Generating (相生): Wood → Fire → Earth → Metal → Water → Wood

Controlling (相克): Wood → Earth → Water → Fire → Metal → Wood

Hidden Stems in Earthly Branches (地支藏干)

Each Earthly Branch contains one or more hidden Heavenly Stems with relative strength weights (main qi / middle qi / residual qi):

City Coordinates Lookup (城市经纬度)

When the user provides a birth city, resolve it to longitude (lng) and latitude (lat) using this table. Do NOT ask the user for coordinates -- look them up here automatically.

If the city is not listed, estimate from a nearby city or use a reasonable default (e.g. provincial capital).

China — Municipalities & Provincial Capitals

China — Other Major Cities

International Cities

Calculation Steps

Reminder: Perform all steps below yourself using arithmetic. Do not call any tool or library.

Step 1: True Solar Time Conversion

Standard Chinese time is based on Beijing (120°E). Adjust for the birth location:

time_offset_minutes = (birth_longitude - 120.0) × 4
true_solar_time = local_time + time_offset_minutes

Step 2: Four Pillars (四柱) — Direct Arithmetic (No Library)

All four pillars are computed with arithmetic and lookup tables. Work through each sub-step in order.

2a. Year Pillar (年柱)

Use the birth year (if the birth date is before 立春 of that year, use the previous year):

year_stem_index   = (year − 4) % 10   → index into Stems list (甲=0 … 癸=9)
year_branch_index = (year − 4) % 12   → index into Branches list (子=0 … 亥=11)

Example: 1990 → stem = (1990−4)%10 = 6 → 庚 ; branch = (1990−4)%12 = 6 → 午 → 庚午年

2b. Month Pillar (月柱)

The Bazi month changes at solar terms (节令), NOT at the lunar new month. Find which month the true-solar-time date falls in using the table below, then derive the stem.

Month Branch by Solar Term:

Month Stem — Five Tiger Trick (五虎遁年起月法):

month_offset      = bazi_month_number − 1      (0 for month 1, 1 for month 2 … 11 for month 12)
month_stem_index  = (five_tiger_start + month_offset) % 10

Example: Year stem 庚 (index 6) → five-tiger start = 4 (戊). Birth in March (Bazi month 2, 卯) → month_stem = (4 + 1) % 10 = 5 → 己. Month pillar: 己卯.

2c. Day Pillar (日柱)

Use the Julian Day Number (JDN) to get a unique integer for each calendar date, then apply the fixed offset.

Step 1 — Compute JDN:

If M ≤ 2: set Y = Y−1, M = M+12
A = floor(Y / 100)
B = 2 − A + floor(A / 4)
JDN = floor(365.25 × (Y + 4716)) + floor(30.6001 × (M + 1)) + D + B − 1524

Step 2 — Day Stem-Branch:

delta            = JDN − 2415021        (2415021 = JDN of 1900-01-01)
day_stem_index   = delta % 10           (甲=0, 乙=1, … 癸=9)
day_branch_index = (delta + 10) % 12    (子=0, 丑=1, … 亥=11)

Verification anchor: JDN 2451545 = 2000-01-01 = 戊午日 (delta=36524, stem=4=戊, branch=6=午).

2d. Hour Pillar (时柱)

1. Map the true-solar-time hour to an Earthly Branch:

   • Hour 23 or 0 → index 0 (子)
   • Otherwise → (hour + 1) // 2

2. Derive the Heavenly Stem using the Five Rat Trick (五鼠遁) from the Day Stem:

hour_stem_index = (zi_start_index + branch_index) % 10

Step 3: Ten Gods (十神)

The Ten Gods describe the relationship between any Heavenly Stem and the Day Master (日主 = Day Pillar's Heavenly Stem).

Algorithm — given Day Stem index d and Other Stem index o:

1. Compute Five-Element indices: d_wx = d // 2, o_wx = o // 2
2. Check polarity: same_polarity = (d % 2) == (o % 2)
3. Compute relation: diff = (o_wx - d_wx) % 5

Step 4: Five Elements Energy Score

For each of the Four Pillars, accumulate scores:

• Each Heavenly Stem contributes 100 points to its element
• Each Hidden Stem in the Earthly Branch contributes its weighted score (see Hidden Stems table above)

Then apply monthly coefficients based on the Month Branch to get seasonal adjustments. The element in season gets a ~2× boost; the element controlled by the season gets ~0.5×.

Step 5: Day Master Strength (日主强弱)

Compute:

• Allies (同党): Elements that are Same-as-me + Produces-me (比劫 + 印)
• Opponents (异党): Elements that I-produce + I-control + Controls-me (食伤 + 财 + 官杀)

If allies score > opponents score → Day Master is Strong (身强) If opponents score > allies score → Day Master is Weak (身弱)

Step 6: Favorable & Unfavorable Elements (用神/忌神)

• Strong Day Master needs to be drained/controlled → Favorable: Food God element, Wealth element, Officer element. Unfavorable: Seal, Companion.
• Weak Day Master needs support → Favorable: Seal element, Companion element. Unfavorable: Food, Wealth, Officer.

Step 7: Major Fortune Cycles (大运)

1. Determine direction: Yang-year + Male OR Yin-year + Female → Forward; otherwise → Reverse
2. Calculate start age: Count days between birth and the next (forward) or previous (reverse) solar term (节); 3 days = 1 year
3. Starting from the Month Pillar, step the Stem-Branch forward or backward for each 10-year cycle

Lite Interpretation Guide

Day Master Personality Profiles

Pattern (格局) Quick Guide

The pattern is determined primarily by the Ten God of the Month Pillar's Heavenly Stem:

Lucky Attributes by Favorable Element

Output Format

When presenting results to the user, structure the output as:

1. Birth Info — Name, date, time, location, true solar time
2. Four Pillars Chart — Year / Month / Day / Hour pillars with Stem, Branch, Hidden Stems, Ten Gods, and Na-Yin
3. Five Elements Analysis — Score breakdown, strongest/weakest element, missing elements
4. Day Master Analysis — Element, strength (strong/weak/balanced), personality tags
5. Favorable Elements — Yong Shen (用神), Xi Shen (喜神), Ji Shen (忌神), lucky colors, lucky directions
6. Major Fortune Cycles — Start age, 10-year cycle Stem-Branch pairs

Advanced Features — Available on Compass AI

This skill covers the core calculation and basic interpretation. For a complete, AI-powered fortune experience, visit:

https://fortune.zodi.zone/web/

Advanced features include:

• AI Deep Analysis — Full personality, career, relationship, and health analysis powered by large language models with streaming output
• Life K-Line Chart (人生K线图) — Fortune scores from age 0 to 100, visualized as an interactive chart showing the highs and lows of each life stage
• Two-Person Compatibility (合盘分析) — Compare two birth charts for love, business, or family compatibility with detailed energy dynamics, conflict points, and synergy analysis
• Daily Fortune Stick (每日灵签) — Personalized daily divination based on your Bazi and the current day's energy
• Interactive Fortune Chat (命理对话) — Multi-turn conversation with an AI fortune-teller that remembers your chart and provides deep, contextual guidance
• Fortune Book Management (命书管理) — Save, compare, and revisit birth charts for yourself and your loved ones

Try it now → Compass AI