Bazica (Ba-zi Chart Calculator)

English · Tiếng Việt

Bazica is a Go library that turns a Gregorian birth time into a Ba-zi (Four Pillars of Destiny, Chinese astrology) chart: the year, month, day and hour pillars, the luck pillars, the yearly pillars, and a layer of derived facts (Ten Gods, life stages, hidden stems, Nayin, stars and more). Every label comes in English and Vietnamese.

Highlights

• Four pillars with the year pillar changing at the instant of Lichun (Start of Spring) and the month at the solar terms, from 1700 to 2399.
• Birth solar term: analysis.birth_solar_term reports bilingual names, the start instant and the next of all 24 terms in the chart's time zone.
• Luck pillars (Da Yun) with their direction, start time, years and nominal ages.
• Yearly pillars (GetAnnualPillars) with Ten God, life stage, the luck pillar a year falls in, and a clash flag.
• Analysis on every chart: Ten Gods, twelve life stages, hidden stems, Nayin, void branches, heaven-clash/earth-clash, 58 verified stars, conception, gestation and life palace pillars, and element counts.
• Bilingual terms with stable codes: every named concept is {code, en, vi}, so a UI can switch language without recalculating.
• No data files to ship: the solar term and Lunar New Year tables are embedded in the module. The tables are generated from the JPL DE440 ephemeris by tools/gencal.
• Careful testing: results are compared with a second implementation and with recorded reference charts (see "Accuracy and checks").

Getting started

Prerequisites

• Go: 1.21 or newer. CI runs the tests on Go 1.21 and on the two most recent releases.

Installing

go get github.com/tommitoan/bazica/v2@latest

and import it:

import "github.com/tommitoan/bazica/v2"

The module path ends in /v2 (Go requires the suffix from v2 on). A plain github.com/tommitoan/bazica import stays on v1.5.0; see "Version 2" below for what changed.

A first chart

package main

import (
	"fmt"
	"log"
	"time"

	"github.com/tommitoan/bazica/v2"
	"github.com/tommitoan/bazica/v2/model"
)

func main() {
	// 1990-12-31 06:30, Ho Chi Minh City, male.
	loc, err := time.LoadLocation("Asia/Ho_Chi_Minh")
	if err != nil {
		log.Fatal(err)
	}
	birth := time.Date(1990, time.December, 31, 6, 30, 0, 0, loc)

	chart, err := bazica.GetBaziChart(birth, loc, model.GenderMale)
	if err != nil {
		log.Fatal(err) // for example model.ErrDateOutOfRange
	}

	p := chart.FourPillar
	fmt.Println("year: ", p.YearPillar.HeavenlyStem.Name, p.YearPillar.EarthlyBranch.Name)
	fmt.Println("month:", p.MonthPillar.HeavenlyStem.Name, p.MonthPillar.EarthlyBranch.Name)
	fmt.Println("day:  ", p.DayPillar.HeavenlyStem.Name, p.DayPillar.EarthlyBranch.Name)
	fmt.Println("hour: ", p.HourPillar.HeavenlyStem.Name, p.HourPillar.EarthlyBranch.Name)
	fmt.Println("day master:", chart.Analysis.DayMaster.HeavenlyStem.Name, "/", chart.Analysis.DayMaster.Element.VI)

	for _, lp := range chart.LuckPillars.LuckPillars[:3] {
		fmt.Printf("luck pillar %d: %s %s, %d-%d\n", lp.Number, lp.HeavenlyStem.Name, lp.EarthlyBranch.Name, lp.YearStart, lp.YearEnd)
	}

	annual, err := bazica.GetAnnualPillars(chart, 2026, 2)
	if err != nil {
		log.Fatal(err)
	}
	for _, y := range annual.AnnualPillars {
		fmt.Println(y.Year, y.NominalAge, y.HeavenlyStem.Name, y.EarthlyBranch.Name, y.TenGod.EN)
	}
}

Output:

year:  Yang Metal Horse
month: Yang Earth Rat
day:   Yang Metal Horse
hour:  Yin Earth Rabbit
day master: Yang Metal / Kim
luck pillar 0: Yang Earth Rat, 1990-1991
luck pillar 1: Yin Earth Ox, 1992-2001
luck pillar 2: Yang Metal Tiger, 2002-2011
2026 37 Yang Fire Horse Seven Killings
2027 38 Yin Fire Goat Direct Officer

GetBaziChart returns a *model.BaziChart that marshals to JSON (json.Marshal(chart)), so it also works as the back end of an API. Luck pillar 0 is the birth month pillar, which applies until the first luck pillar starts. Runnable examples with tested output are in example_test.go and on pkg.go.dev.

Birth range and data

Birth dates from January 1, 1700, to December 31, 2399 are supported. bazica.SupportedYears() returns the first and last year, taken from the embedded calendar tables; dates outside the range return model.ErrDateOutOfRange.

The solar term and Lunar New Year tables are embedded in the module (go:embed), so nothing has to be copied into your project and the library works from any working directory, including a vendored build or a container image with only the binary. The same tables are published as JSON in the data folder if you want to use them elsewhere:

• data/solar-term.json: the 24 solar terms for each year, in UTC.
• data/lunar-new-year.json: the Lunar New Year date for each year. It feeds only the display-only year_reference block; no pillar is calculated from it.

Version 2

v2.0.0 changes the module path to github.com/tommitoan/bazica/v2 (Go requires the suffix from v2 on); no function or type was renamed or removed, so updating means changing the import path and running go get github.com/tommitoan/bazica/v2@latest. v1.5.0 stays available for anyone who wants the previous behaviour.

What changed in the results. The year pillar now changes at the instant of Lichun instead of the Lunar New Year, the way solar-term Ba-zi calculators do. Charts for births outside the two windows below are unchanged (a test compares 658 of them with v1.5.0). For a birth between the Lunar New Year and Lichun, or between Lichun and the Lunar New Year (about 2 % of births, 7.4 days a year on average, 16 at most), these change:

• the year pillar and everything derived from it (Ten God, hidden stems, life stage and Nayin of the year pillar);
• the stars: a star changes when its rule starts from the year pillar or when it lands in the year or month pillar, which covers most of the table. In a check of every such day of 1901-2099, both genders, every chart had at least one different star and 39 star terms were involved, so treat the stars of these births as new;
• the month stem (the month branch follows the solar term as before);
• the direction and the sequence of the luck pillars, because the year stem's polarity decides the direction, and the first row of the yearly table with the nominal age.

The day and hour pillars never change. The results were checked against a second implementation (lunar-javascript) for every such day of 1901-2099, both genders: four pillars, first luck pillar and luck direction (testdata/calendar/lunarjs-window-1901-2099.json).

What was added. analysis.year_reference reports, for every chart and for display only, the Lichun time of the birth's civil year (in the birth zone), the year of the lunar calendar with its stem, branch, zodiac animal and Lunar New Year date, and differs, which is true when that lunar-calendar year is not the year pillar. Nothing is calculated from it; a test guards that.

The lunar-calendar year follows the Lunar New Year table, which holds one date per year and follows the Chinese calendar (UTC+8), whatever loc you pass. Vietnam's calendar (UTC+7) places the Lunar New Year on another day in some years: in 1900-2099 these are 1903, 1935, 1965, 1968, 1969, 1985, 2007, 2030 and 2053 (tools/gencal/README.md has the comparison; later years were not checked). On that one day of such a year, lunar_year and differs can disagree with a Vietnamese almanac. No pillar is affected, because the year pillar follows Lichun.

Analysis

From v1.4.0 every chart also carries derived facts under an analysis key. The fields that existed in v1.3.0 are unchanged, and every added key is named analysis, so existing clients keep working.

Where	Field	Meaning
each natal pillar	ten_god	stem against the Day Master (null on the day pillar)
	stem_element, branch_element, nayin	five elements and the Nayin
	stem_stage_at_own_branch, stem_stage_at_month_branch, day_master_stage	the twelve life stages
	hidden_stems	stems hidden in the branch, main qi first, each with its Ten God and stage
	is_void, heaven_earth_clash	void branch and clash flags
	stars	the 58 verified stars, in a fixed order (empty list when none); each carries nature (see below)
each luck pillar	age_start, age_end	nominal age range
	ten_god, nayin, stem_stage_at_own_branch, hidden_stems, heaven_earth_clash	as above
chart	day_master, void_branches	the Day Master and the two void branches
	year_reference	display only: the Lichun time of the birth year, the year of the lunar calendar (stem, branch, zodiac animal, Lunar New Year date) and differs (see "Version 2")
	thai_nguyen, thai_tuc, life_palace	conception, gestation and life palace pillars with their Nayin
	element_counts	unweighted counts of stems, branches and hidden stems per element
	weighted_elements	eight points split across exposed stems and weighted hidden stems, with levels, Ten God subtotals and source contributions
	pattern_candidates	preliminary month-branch qi candidates, including exposure evidence; these are not final patterns
	day_master_strength,

weighted_elements.scheme is hidden_stems_v1: each exposed stem scores 1; each branch scores 1, split across its ordered hidden stems as 1, 0.7/0.3 or 0.6/0.3/0.1. level_scheme is score_levels_v1: levels 0–4 use cutoffs 0.5, 1.5, 2.5 and 3.5. These levels are a display convention, not a strength or useful-god judgement. The Day Master's own exposed stem is included in its element score as day_master: 1, but has no Ten God; all Ten God subtotals therefore sum to 7. Both Ten Gods belonging to an element are always present, including a zero score. Each element includes its per-pillar contributions so clients can audit the result.

pattern_candidates examines the month branch's hidden stems and reports any revealed among the year, month and hour stems. If none are revealed it reports the main qi as a weaker candidate. Multiple revealed qi remain multiple candidates. A peer candidate requires a separate special-pattern review. The field does not resolve combinations, transformations or final pattern selection. Neither it nor weighted_elements determines useful_god by itself.

Every named concept (Ten God, life stage, element, polarity, Nayin, star) is an object with a stable code and an English and a Vietnamese label:

{"code": "ten_god.hurting_officer", "en": "Hurting Officer", "vi": "Thương Quan"}

Switch on code, not on a label. A UI can show either language without recalculating the chart.

GetAnnualPillars(chart, fromYear, count) returns the pillar of each year with its Ten God, life stage, nominal age, the luck pillar it falls in and the clash flag:

chart, _ := bazica.GetBaziChart(birth, loc, model.GenderMale)
annual, err := bazica.GetAnnualPillars(chart, 2026, 10)
if err != nil { // model.ErrInvalidYearRange
	return err
}
for _, y := range annual.AnnualPillars {
	fmt.Println(y.Year, y.NominalAge, y.HeavenlyStem.Name, y.EarthlyBranch.Name, y.TenGod.EN)
}

fromYear may not precede the year pillar's year or the first supported birth year (see SupportedYears), and the years must not pass 9999. The yearly table is not limited to the range of a birth date: each year's pillar is the sixty-year cycle, so it continues after 2399 (a luck pillar number is null once a year is past the twelfth luck pillar).

Analysis conventions

• Nominal age: the year of the year pillar is age 1. For a birth before Lichun the year pillar belongs to the previous year, so ages count from there. This is the Ba-zi count, not the everyday count from the Lunar New Year.
• Stars: only stars whose rules were verified against reference charts are reported (58 stars, checked on 298 recorded charts and 10,000 random births against an independent implementation). Other stars are never guessed. Several rules differ from the classical tables because they follow the reference page, for example Red Allure (hong_diem) reads both the day stem and the year stem, and Great Depletion (dai_hao) depends on gender.
• Star nature: each star term has an optional nature key, set on stars only: auspicious (cát), inauspicious (hung) or mixed (tùy cục, the effect depends on the rest of the chart). It is a hint for display. Schools disagree about what is favourable and many stars cut both ways, so the value is not a judgement of the chart. The reference page labels stars only good or bad; the library follows it except for 10 stars it reads as mixed and one (am_duong_sat) it reads as inauspicious where the page says good. Other terms (Ten Gods, stages, elements, Nayin) never carry the key. It is additive: a client that ignores it keeps working.
• Moon General (thai_duong): the general changes at each principal term, and the whole calendar day on which a term falls already has the new general. The reference page dates a few terms one day off, so on a term day the result can differ from the page by one day.
• Life palace: Rat and Ox are counted before Tiger when the stem is derived, which differs from the classical month order.
• Heaven-clash/earth-clash: directional. A cell is flagged when its stem overcomes another natal pillar's stem with the same polarity and their branches are opposite. Earth stems take part.
• Strength and Useful God: not computed.

Conventions

• Day: the day changes at 23:00 (the Rat hour), so a birth at 23:30 takes the pillar of the next day.
• Year: the year changes at the instant of Lichun (Start of Spring), the same solar-term clock as the month; the comparison uses the exact instant, so the 23:00 day rule does not apply to it.
• Month: the month changes at the "initial" solar terms (jie), such as Start of Spring and Awakening of Insects. The month stem follows from the year stem by the Five Tigers rule.
• Birth solar term: analysis.birth_solar_term is the interval between consecutive instants among all 24 terms. It is display-only; a midpoint term such as Winter Solstice does not open a new month pillar. Early January can fall in Winter Solstice while the month pillar still belongs to the month opened at Major Snow.
• Lunar-calendar year (reference): the year that changes at the Lunar New Year, reported under analysis.year_reference for display only. It follows the civil date (the lunar calendar changes year at midnight, so the 23:00 day rule does not apply to it). For a birth between the Lunar New Year and Lichun it differs from the year pillar.
• Time zone: dateTime is read as wall-clock time in loc, so pass the birth place's zone. A nil loc keeps the zone dateTime already carries.
• Gender: 0 is female and 1 is male (model.GenderFemale, model.GenderMale); it sets the direction of the luck pillars. Other values return model.ErrInvalidGender.

Accuracy and checks

The two tables (data/solar-term.json and data/lunar-new-year.json) are generated by tools/gencal from the JPL DE440 ephemeris, which also says how and how accurately. Lunar New Year follows the Chinese calendar (UTC+8, and Beijing mean time before 1929). The accuracy of a solar term depends on Delta T, the difference between uniform time and Earth's rotation: it is reconstructed from observations up to the present, so terms are good to a few seconds from 1700 to 2025, and a prediction after that, so the uncertainty grows to minutes by 2399. A check against a second, independent package (a different method and its own Delta T) agrees within about a minute from 1700 to 2000; after 2100 the two Delta T predictions differ by 3 to 5 minutes, so a birth within about five minutes of a solar term is uncertain there, and so are the Lunar New Years of 2299 and 2333. A birth within that margin of a solar term, Lichun included, may get the neighbouring month or year pillar. The Lunar New Years of 2299 and 2333 are as uncertain, and they only affect the display-only lunar-calendar year.

Before about 1900 many places used local mean time. bazica reads the wall-clock time in the loc you pass, so pass the zone (or fixed offset) that was in use at the birth place.

If you require calculations for dates outside the supported range, please consider alternative libraries or solutions.

Ho Chi Minh City 1975

Ho Chi Minh City (formerly Saigon) has gone through time zone changes throughout history. Notably: Before 1975: South Vietnam (including Saigon) used UTC+8. After 1975: The unified Vietnam adopted UTC+7.

The web app

This library powers bazi.tommitoan.com, a free Ba-zi chart page in Vietnamese and English. The web app's source is private, and it has no Ba-zi logic of its own: it validates the request and calls GetBaziChart and GetAnnualPillars, so everything it shows is a field documented on this page. If you want to see what the data looks like in use, this is the quickest way.

What the page shows:

• the four pillars with their full facts and every star, one per line;
• the Five Elements diagram, with a bar for each element coloured by its weighted score (weighted_elements): red below 0.5, a pale green that deepens at each level cutoff, and a nearly black green at 4.5;
• the luck pillars and a card for each of sixty years, with the viewed year highlighted;
• shareable chart links and an optional PDF export;
• a dark look and a light, aged-paper look, following the system setting or a button.

The same look continues on the author's site: tommitoan.com/fengshui tells the story of a chart as one scroll, from a falling star to the four pillars, and leads to the web app.

Development

go test -race -cover ./...
gofmt -l .
go vet ./...

tools/gencal regenerates the two calendar tables; its README explains the method and the checks.

References

This project drew inspiration and information from the following sources:

• Thời Gian - A comprehensive resource for understanding the Vietnamese calendar system.
• Chinese Fortune Calendar - Provided insights into the Chinese calendar, calculations, and cultural significance.
• Understand the Chinese Lunar and Xia calendar in Ba-zi - A discussion of the lunar and Hsia (seasonal, solar term) calendars used to read the Four Pillars. Bazica follows the solar-term calendar for both the year and the month since v2.0.0; v1 changed the year at the Lunar New Year.

License

MIT, see LICENSE.