Chinese astrology: one birth date, four systems, and what each can actually tell you

Here is the family at a glance. Each row takes something from your birth, gives something back, and has a page on this site that shows its working.

The thing to notice is the first column. Not one of the four looks at the sky on the night you were born. Western astrology begins with the planets; Chinese astrology begins with a calendar, and the calendar is the oldest part of it by a thousand years.

Consider what a Chinese astrologer is actually holding when they hold your chart. It is eight characters, and every one of them comes from a set of twenty-two: ten heavenly stems and twelve earthly branches, paired off in step until sixty pairs have gone by and the first comes round again. The sixty were not invented for fortune-telling. They were invented for counting days. The oracle bones of the Shang kings, the oldest Chinese writing there is, already carry the full cycle of sixty day-names by about 1200 BC, and, as the calendar historian Zhang He points out, the kings themselves carried stem names, Father Yi, Grandfather Ding, like days of the week. The names were applied to years, and then to months and hours, only much later, "at least since the Han," in Zhang's phrase. A stem-branch day count has run without a break from then to this morning; the sexagenary cycle page walks it back to an eclipse in 720 BC.

The animals came last. The twelve branches had been counting for a thousand years before anyone attached a Rat to the first of them; the earliest list that pairs branches with animals is on bamboo slips from Qin-dynasty tombs in Gansu, by the second century BC, and the first writer to argue with the pairing is Wang Chong, around AD 80, in a chapter of his Lunheng that runs through the animals to make fun of the five-element theorists. Nothing in that chapter says an animal describes a person. The Huainanzi, a Han compendium from before 139 BC, does the other half of the work in a single sentence, assigning every stem and every branch to one of the five elements, wood, fire, earth, metal and water, and that sentence is the reason a Metal Horse is metal and a horse. Two systems of counting, one very old and one merely old, laid on top of each other: that is the material. Everything below is a way of reading it.

Your Chinese zodiac sign is the branch of your birth year, wearing its animal, and your year element is that year's stem. That is the whole mechanism, with one catch that trips up a surprising share of the people who search for their sign: the year does not start on January 1. It starts at Chinese New Year, on the second new moon after the winter solstice, anywhere from January 21 to February 20, so a January birthday almost always belongs to the animal before. The zodiac calculator applies the exact date for every year from 1900 to 2100 and prints the element, the sixty-cycle name and the sound along with the animal.

The sign is one of eight characters, the one you share with every person born in the same twelve months, and it describes none of them in particular: the classical manuals attach no temperament to any year at all: the reputations, the loyal Dog and the restless Horse, are folk tradition with a long and cheerful history and no source behind them older than the tradition itself. The tables that do have a source are the ones about relations between signs, trine, harmony, clash and harm, which the compatibility checker applies to all 66 pairings with the rule shown. The one thing a birth year settles for certain is which of the twelve you will be told to wear red for, when your own animal's year comes back.

The system most people mean by Chinese astrology proper is bazi, "eight characters," also called the four pillars of destiny: the stem and branch of your year, month, day and hour, laid side by side and read against one another. It has a founding date that can be stood next to a grave. In 813 a palace censor named Li Xuzhong died at fifty-two, was buried outside Luoyang, and had his epitaph written by his friend Han Yu, the most celebrated prose writer of the Tang. Li was deep in the books of the five elements, Han Yu says, and could take the stem and branch of a person's birth year, month and day, weigh which elements were flourishing and which exhausted, and pronounce on long life or short, honor or obscurity, fortune or its absence, missing not one or two cases in a hundred. That is the earliest description of the method by a witness, and it has a hole in it you could drive a cart through: three pillars, not four. There is no hour.

The hour, and the whole modern method, arrived in the Song, and we know because the Qing dynasty's own librarians said so in print. When the compilers of the Siku Quanshu, the imperial catalog of 1782, examined the book that circulates under Li Xuzhong's name, they found its first half discussing the sixty pairs with no birth hour anywhere, matching Han Yu's epitaph exactly, and its second half full of "the four pillars," which, they wrote, is a method that in fact arose in the Song. Somebody had stitched a newer system onto an older name. The catalog printed the book anyway, and flagged the forgery paragraph by paragraph. Their entry on a second text says the same thing more bluntly: at the time of Li Xuzhong the reckoning still began only from the year, month and day; there was not yet any such thing as "eight characters."

The name attached to the Song upgrade is Xu Ziping, and here the record does something the fortune-telling websites never mention. The same catalog says Ziping's life cannot be traced, that his method is nonetheless what the whole trade follows, and that reckoning the eight characters is called "Ziping" simply because of him. It then reports the story that went round about him, that he was a hermit who hid on Mount Hua with the Daoist immortal Lü Dongbin and with Chen Tuan, and dismisses it in one sentence: of the sayings of the diviners' trade, not one in a hundred is true, and there is no way to press them. What Ziping's method actually changed is the thing that makes bazi bazi. Li Xuzhong read a life from the year. The Song method reads it from the day, the stem of the day you were born, and treats the other seven characters as the weather around that one. The Yuanhai Ziping, the founding manual of the school, sets the rule, and every reading since has followed it, including the one walked through step by step on this site.

The book that settled the method for everyone after was the Sanming Tonghui of 1578, twelve chapters by a Ming official named Wan Minying, and the Qing catalog's verdict on it is the best one-line history of the subject: since the Ming, everyone discussing fate has used it as the compendium, and nearly every household owns a copy. The same entry notes, with a librarian's sigh, that some of its theories, applied today, frequently fail to verify. That sentence was written in 1782. It is where the last section of this page begins.

Bazi has a rival that answers the same question with a completely different instrument. Zi wei dou shu, "purple star reckoning," takes your lunar birth month, day and hour and lays out twelve palaces, one each for life, siblings, spouse, children, wealth, health, travel, friends, career, property, fortune and parents, then drops named stars into them: the Purple Star that gives the system its name and plays the emperor, the Sun, the Moon, the Wolf, the Army-Breaker, fourteen major ones and a crowd of minor. None of them is a star you could point a telescope at. They are positions in a table, placed by arithmetic from the birth data. The chart looks like a horoscope and works like a spreadsheet.

Its origin is a legend with a familiar name in it. The system is traditionally credited to Chen Tuan, the same tenth-century hermit of Mount Hua that the Ziping story hides Xu Ziping with, which tells you more about how Chinese fortune-tellers claimed ancestry than about either system. The earliest texts anyone can date are from the sixteenth century, the same generation as the Sanming Tonghui, and the schools that read it today are modern. Where bazi weighs elements, zi wei reads a map: which palace a star landed in, which palaces face each other across the chart. The comparison page puts the two side by side on one birth date and says when a reader would reach for each.

The fourth system is not about time at all. Feng shui's kua number takes your birth year and your sex and returns one of eight trigrams, the three-line figures of the Book of Changes, and with it four favorable compass directions and four unfavorable ones. The trigrams' directions come from the Shuo Gua, the ancient commentary on the Changes that stations each figure at a point of the compass; the method of turning a birth year into one of them, the "eight mansions" school, was codified in a Qing manual, the Bazhai Mingjing, and is the piece of feng shui a person can carry with them, since the number belongs to you and not to the house. It is astrology in the strict sense of being born from a birth date, and geography in every other sense.

Two things connect it to the rest of the family. The year it uses turns at Lichun, the solar start of spring around February 4, the same boundary a bazi chart uses and not the Chinese New Year the zodiac follows, so a person born in the first days of February can have a different year in their kua than in their sign. And the five elements it works in are the same five the Huainanzi assigned to the stems and branches. The feng shui pages take it from there, room by room, and the 2026 page reads this year's chart in space the way the zodiac page reads it in time.

The word "astrology" is doing two jobs in English and it is worth pulling them apart. Western astrology is a snapshot of the sky. A natal chart is where the sun, moon and planets stood, seen from your birthplace at your birth minute, against the twelve signs of the ecliptic; it needs a place as well as a time, and it is, in principle, a statement about the heavens that an astronomer could check. Chinese astrology is a calendar. A bazi chart needs no place at all, because the stem and branch of a day are the same in Beijing and Boston; the sky enters only through the year, whose twelve branches were tied, in the Huainanzi, to the twelve-year circuit of Jupiter, and even that link loosened once the count was left to run on its own.

The second difference is what each is for. A natal chart is read for character, the kind of person the placements make you. A bazi chart can be read that way too, and usually is, but its native question is "when." The engine of the system is the luck pillars, ten-year stretches assigned from the month of birth and read one after another across a whole life, with the current year laid over the top, so that the tradition's actual output is a timeline: which decades favor you, which years to hold still in, the arithmetic of which is on its own page. Western astrology has transits and progressions, but they are an extension; in bazi, timing is the point. A zi wei chart, for what it is worth, sits nearer the Western shape, a map of palaces read for who you are, which is one reason it has an easier time crossing over.

The third difference is the one this site is built on. A Western chart with a full time and place is unique to you; a Chinese sign is shared by everyone born in the same year, and even a full bazi chart, eight characters from a set of sixty pairs, has only about half a million possible forms, so many thousands of people alive carry yours. The tradition never pretended otherwise. What it claims is not that the chart is you but that it is the weather you were born into, and that the weather can be read.

Split the question in three and it answers itself. The first part is the calendar, and the calendar is exact. The stems and branches of every day on this site are computed astronomically, the year turns at the minute Lichun occurs and the Chinese New Year dates match the Hong Kong Observatory's; if two calculators disagree about your chart, one of them has the calendar wrong, and that is a checkable error, not an opinion. This is the part of Chinese astrology that is simply true, and it is a larger part than people expect, because a great deal of what goes wrong in casual readings is a January birthday given the wrong year.

The second part is what the charts are said to predict, and here the honest answer is that almost none of it has been tested, and the one piece that has did not pass. The Qing gender chart, which claims to predict a baby's sex from the mother's age and the month of conception, was run against 2.8 million Swedish births by the epidemiologist Eduardo Villamor and colleagues in 2010 and came out right about half the time, at every age and in every month, which is what a coin does. No study of comparable size has ever been run on bazi, and the tradition is arranged so that none easily could: a reading's central move, deciding whether the day master is strong or weak, follows conventions that differ from one school to the next, and this site's own conventions page documents how far published charts of the same person diverge. A method whose practitioners cannot agree on the first step of a reading cannot be scored on the last. That is simply what the record shows, and it is also, as it happens, what the tradition's own custodians said: Han Yu's claim for Li Xuzhong, not one case in a hundred missed, is a thousand years old, and the imperial librarians who read the same books nine centuries later wrote that of the trade's claims not one in a hundred was true, and that the most popular manual in the country frequently failed to verify.

The third part is what it is good for, which is the part the studies cannot see. A bazi chart is a thousand-year-old vocabulary for thinking about a life in stretches of ten years, with a built-in insistence that no period is permanent and that the same person is favored in one decade and exposed in the next. People find that useful in the way they find a good question useful, and a reader who treats the chart as a structured conversation rather than a forecast is using it the way the better practitioners always have. On this site the readings show their arithmetic, name their sources and say what they cannot know; the gender chart page tells you it is a coin, and the bazi pages tell you where the conventions begin. That is the most accurate thing a page on this subject can be.