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Bazi Four Pillars (八字)

Builds the Bazi (八字, Bāzì) / Four Pillars (四柱) chart of a birth date and time: year pillar by 立春 (Lìchūn), month pillar by the 节 (jié) solar terms, day pillar from the sexagenary day count, hour pillar by the 五鼠遁 (Wǔshǔdùn) rule, plus day master, five-element counts, ten gods (十神), hidden stems (藏干), 纳音 (nàyīn), void branches (空亡) and the ten-year luck pillars (大运).

Birth dateGregorian civil date of birth in the local clock time of the birthplace (1900–2100). Birth timeLocal clock time of birth, 24-hour HH:MM. 23:00–00:59 is 子时 (Zǐ hour). SexSex, used only for the direction of the luck pillars (阳年男/阴年女 forward, 阴年男/阳年女 backward). UTC offset of the clock time (h) (optional)Time-zone offset of birth_time in hours (China Standard Time = 8; use the historical zone in force at birth). Birthplace longitude (°) (optional)Optional east-positive longitude. When given, the clock time is converted to true solar time: correction = (longitude − 15 × utc_offset_hours) × 4 min + equation of time. Late 子时 belongs to the next day (optional)true: 23:00–23:59 belongs to the next day's 子时 and the day pillar advances at 23:00. false: 晚子时 convention — the day pillar stays, only the hour stem is taken from the next day. Include hidden stems (optional)Add the hidden stems (藏干) of the four branches to the element count with weights 1.0 (main), 0.5 (middle) and 0.3 (residual).

When to use

You need the four stem-branch pillars (年柱月柱日柱时柱) of a birth moment, the day master and its ten-god relations, element balance, or the start age and sequence of the 大运 luck pillars.

Do not use when: You only need the lunar date or zodiac of a date (use lunar-calendar-converter or chinese-zodiac), the stem-branch of a single date without an hour (use sexagenary-cycle), or an interpretation of the chart — this tool computes the traditional chart only and gives no predictions.

Formula

year = solarYearAtLichun(birth instant); month stem = ((year stem mod 5) × 2 + 2 + months since 寅) mod 10; day index = (JDN + 49) mod 60; hour stem = ((day stem mod 5) × 2 + hour branch) mod 10; hour branch = floor(((hour + 1) mod 24) / 2); true solar time = clock + (longitude − 15 × utc_offset) × 4 min + equation of time; 起运 years = days to 节 / 3

Sexagenary pillars per the Chinese calendar convention (GB/T 33661-2017 solar terms computed from Meeus' VSOP87 series, civil days at UTC+8); the birth instant is compared with the exact term instants, so births on a term day before the term keep the previous month/year. Traditional reference calculation of the Chinese calendar tradition; not a prediction and not medical, legal or financial advice.

Inputs

Parameter	Type	Unit	Required	Description
`birth_date`	date		yes	Gregorian civil date of birth in the local clock time of the birthplace (1900–2100).
`birth_time`	string		yes	Local clock time of birth, 24-hour HH:MM. 23:00–00:59 is 子时 (Zǐ hour).
`sex`	enum: male \| female		yes	Sex, used only for the direction of the luck pillars (阳年男/阴年女 forward, 阴年男/阳年女 backward).
`utc_offset_hours`	number	h	default 8	Time-zone offset of birth_time in hours (China Standard Time = 8; use the historical zone in force at birth). Range: ≥ -12, ≤ 14
`longitude_degrees`	number	°	no	Optional east-positive longitude. When given, the clock time is converted to true solar time: correction = (longitude − 15 × utc_offset_hours) × 4 min + equation of time. Range: ≥ -180, ≤ 180
`late_zi_next_day`	boolean		default true	true: 23:00–23:59 belongs to the next day's 子时 and the day pillar advances at 23:00. false: 晚子时 convention — the day pillar stays, only the hour stem is taken from the next day.
`include_hidden_stems`	boolean		default true	Add the hidden stems (藏干) of the four branches to the element count with weights 1.0 (main), 0.5 (middle) and 0.3 (residual).

Outputs

Output	Type	Unit	Description
`bazi_chart`	string		The eight characters in the order year, month, day, hour.
`year_pillar`	string		Stem-branch of the year; the year changes at 立春 (Start of Spring), not at Chinese New Year.
`month_pillar`	string		Stem-branch of the solar month, which starts at each 节 (odd solar term); stem by 五虎遁 (Wǔhǔdùn).
`day_pillar`	string		Stem-branch of the birth day (continuous 60-day count; 2000-01-01 = 戊午).
`hour_pillar`	string		Stem-branch of the double-hour; stem by 五鼠遁 from the day stem.
`pillars_pinyin`	object		Pinyin of the four pillars.
`pillars_english`	object		Stem element + branch animal of each pillar, e.g. Fire Horse.
`day_master`	string		The day stem, its pinyin, polarity and element; all ten-god relations are taken from it.
`zodiac`	string		Animal of the year pillar branch (立春 boundary).
`five_element_counts`	object		Raw counts of Wood/Fire/Earth/Metal/Water over the 8 characters; with include_hidden_stems also weighted counts that add hidden stems at 1.0/0.5/0.3.
`missing_elements`	string_list		Elements absent from the 8 visible characters (empty list when all five are present).
`dominant_element`	string		Element with the highest raw count (ties listed together).
`ten_gods`	object		Relation of each other stem, and of the main hidden stem of each branch, to the day master.
`hidden_stems`	object		Hidden stems of each pillar's branch in main/middle/residual order.
`nayin`	object		Nayin melodic element of each pillar.
`void_branches`	string		The two branches not covered by the day pillar's 旬 (xún, ten-day decade).
`luck_direction`	string		Forward (顺行) for yang-year males and yin-year females, backward (逆行) otherwise.
`luck_start_age`	string		Age at which the first luck pillar begins: days from birth to the next (forward) or previous (backward) 节 converted at 3 days = 1 year, 1 day = 4 months.
`luck_start_age_years`	number	years	The same start age as a decimal number of years (days to the 节 ÷ 3).
`luck_pillars`	list		Eight ten-year luck pillars with start age (completed years) and calendar year; forward = following month pillars, backward = preceding ones.
`lunar_birth_date`	string		Chinese lunar calendar date of the birth day.
`solar_term_context`	string		The 节 governing the month pillar and the next 节, in China Standard Time.
`time_used`	string		The birth time actually used for the pillars (true solar time when a longitude is given).
`notes`	string_list		Conventions applied to this chart.

Example

1990-05-17 08:30 Beijing time, male: {"birth_date":"1990-05-17","birth_time":"08:30","sex":"male","utc_offset_hours":8} → {"year_pillar":"庚午","month_pillar":"辛巳","day_pillar":"壬午","hour_pillar":"甲辰","day_master":"壬 Ren — Yang Water (水)","pillars_english":{"year":"Metal Horse","month":"Metal Snake","day":"Water Horse","hour":"Wood Dragon"},"five_element_counts":{"wood":1,"fire":3,"earth":1,"metal":2,"water":1},"missing_elements":[],"void_branches":"申酉 (Shen, You — Monkey, Rooster)","luck_direction":"forward (顺行): yang year, male","luck_start_age":"6 years 7 months","luck_start_age_years":6.64,"luck_pillars":[{"start_age":6,"pillar":"壬午"},{"start_age":16,"pillar":"癸未"},{"start_age":26,"pillar":"甲申"},{"start_age":36,"pillar":"乙酉"},{"start_age":46,"pillar":"丙戌"},{"start_age":56,"pillar":"丁亥"},{"start_age":66,"pillar":"戊子"},{"start_age":76,"pillar":"己丑"}],"lunar_birth_date":"一九九〇年四月廿三 (lunar year 1990, month 4, day 23)"}

2000-01-01 00:30 Beijing time, female (before 立春 2000): {"birth_date":"2000-01-01","birth_time":"00:30","sex":"female","utc_offset_hours":8} → {"year_pillar":"己卯","month_pillar":"丙子","day_pillar":"戊午","hour_pillar":"壬子","day_master":"戊 Wu — Yang Earth (土)","five_element_counts":{"wood":1,"fire":2,"earth":2,"metal":0,"water":3},"missing_elements":["Metal (金)"],"void_branches":"子丑 (Zi, Chou — Rat, Ox)","luck_direction":"forward (顺行): yin year, female","luck_start_age":"1 year 9 months","luck_pillars":[{"start_age":1,"pillar":"丁丑"},{"start_age":11,"pillar":"戊寅"},{"start_age":21,"pillar":"己卯"},{"start_age":31,"pillar":"庚辰"},{"start_age":41,"pillar":"辛巳"},{"start_age":51,"pillar":"壬午"},{"start_age":61,"pillar":"癸未"},{"start_age":71,"pillar":"甲申"}],"ten_gods":{"year_stem":"己 → 劫财 (Jiecai, Rob Wealth)","month_stem":"丙 → 偏印 (Pianyin, Indirect Resource)","hour_stem":"壬 → 偏财 (Piancai, Indirect Wealth)"}}

GET https://tttkmbb.com/api/v1/calculate/bazi-four-pillars?birth_date=1990-05-17&birth_time=08%3A30&sex=male&utc_offset_hours=8

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/bazi-four-pillars (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/bazi-four-pillars · Markdown: https://tttkmbb.com/lunar/bazi-four-pillars.md · JSON definition: https://tttkmbb.com/lunar/bazi-four-pillars.json
MCP: server https://tttkmbb.com/mcp, tool calculate_bazi_four_pillars
OpenAPI operationId: calculate_bazi_four_pillars
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Four Pillars of Destiny (Wikipedia) (reference)
Sexagenary cycle (Wikipedia) (reference)
Hong Kong Observatory – Gregorian-Lunar Calendar Conversion Table (government)

FAQ

Why does the year pillar differ from the Chinese New Year zodiac?

Bazi years begin at 立春 (about 4 February), not at Chinese New Year, so a birth on 2000-01-01 belongs to the 己卯 year although the 庚辰 lunar year would begin on 2000-02-05.

What happens at 23:00?

With late_zi_next_day = true (default) the day pillar and hour pillar are taken from the next day at 23:00. With false the day pillar stays and only the hour stem is derived from the next day's stem (晚子时 convention).

Should I enter the longitude?

Practitioners who use true solar time enter it: the clock time is shifted by 4 minutes per degree from the zone meridian (120° E for UTC+8) plus the equation of time (−14 to +16 minutes over the year). Leave it empty to use clock time.

Related calculators

Chinese Almanac Day (黄历) — Day officer, spirits and taboos of any date in the same calendar.
Sexagenary Cycle Calculator (干支) — Stem-branch of a date without the hour pillar.
Chinese Double-Hour Calculator (时辰) — Double-hour (时辰) of a clock time.