The sixty-year wheel

Ten stems ride twelve branches, the sun picks the leap month, and the day-count has not skipped a beat in over two thousand years. ← Calendar Contraptions

The Hebrew calendar of the last piece reconciles three clocks with a rulebook; the Chinese one reconciles them with a machine that is still running. Months begin on the day of a new moon. Seasons are marked by twenty-four solar terms — the sun's own ruler, fifteen degrees of sky at a time. And the year is whatever the two agree on: an extra month is inserted wherever the sun's marks leave a month unclaimed. On top of it all rides a wheel of sixty names — wooden rats, fire horses, metal goats — that has counted the days without a single interruption since the Zhou dynasty.

Pick a date. The machine reads it back the way a traditional almanac would — and shows you the clockwork that decided the answer.

The sun's clockwork

Here is the rule that makes the calendar lunisolar. The winter solstice must always fall in month 11. Walk the months forward from one winter solstice to the next: if twelve complete months fit between the two solstices, nothing is added. If thirteen fit — which happens seven times in nineteen years — the first month that contains no major solar term becomes the leap month, and borrows the previous month's number with a 閏 (rùn, intercalary) in front of it. The moon decides where the months sit; the sun decides where the extra one goes. The result is a year of wildly uneven length: common years run 353, 354 or 355 days, and leap years 383, 384 or 385 — in the table behind this page, exactly one common year of 353 days (the 1965 year, which ended on the calendar's earliest New Year) and three leap years of 385.

The sixty-year wheel

Years, months and days each carry a name made of two characters: one of ten heavenly stems (甲乙丙丁戊己庚辛壬癸 — jiǎ, yǐ, bǐng, dīng, wù, jǐ, gēng, xīn, rén, guǐ) paired with one of twelve earthly branches (子丑寅卯辰巳午未申酉戌亥). Both wheels turn together, so the pair repeats only every sixty steps — the least common multiple of ten and twelve. Half of all 120 possible pairs never occur: odd stems always meet odd branches, even meets even. The wheel is called 六十花甲, liùshí huājiā — "sixty flowered armors". Each stem carries one of the five elements doubled (wood, fire, earth, metal, water — each once yin, once yang), which is where "wood rat" and "fire horse" come from.

Find your animal

Type the year you were born. The animal changes at Chinese New Year, not on January 1st — so if your birthday falls before New Year, the machine corrects you.

Where the calendar gets its teeth

One date, two year pillars. The almanac year changes at Chinese New Year. But the fortune-tellers' year pillar changes at 立春 (Lìchūn, "spring begins", around February 4th) — the solar term, not the New Year. And the month pillar follows the sun's months, not the moon's: it flips at each minor solar term, so early February still belongs to the old year's tiger month even after the New Year has begun. When the two conventions disagree for your date, the pillars row above says so.

New Year's wandering day

Chinese New Year is the second new moon after the winter solstice (the third, in the rare years when a leap month crowds the tail of the previous year). Between 1901 and 2099 the date has wandered from January 21st — in 1966, 2061 and 2099 — to February 20th, in 1920 and 1985. Two folk rules track it: "the new moon closest to Lìchūn" and "the first new moon after Dàhán (Great Cold)". Both are right most years and wrong in a handful — the real rule is the solstice-in-month-11 machine, not the approximations.

The year-to-year dance has a rhythm: if New Year fell in February, the next one usually lands 10, 11 or 12 days earlier; if it fell in January, the next one always leaps forward 18, 19 or 20 days. (The "usually" is honest: three years in the table — 1919, 1984, 2052, all New Year on February 1st or 2nd — bucked the February rule and leapt forward instead.) That is just the 354-day lunar year (10–11 days short) versus the 384-day leap year (19 days long) seen from outside.

Where you stand changes the date

The whole machine runs on local time — and local time is a political choice. The most famous consequence: in 1968, the first new moon of the year fell at 16:29 UTC on January 29th. North Vietnam counted in UTC+7 and began Tết at 23:29 that evening; South Vietnam counted in UTC+8 and began it just after midnight, on January 30th. The two halves of a country at war celebrated the same holiday a day apart — close enough that the Tet Offensive's attacks landed on different calendar days on different sides.

Vietnam keeps a calendar built the same way on its own meridian; its zodiac replaces the rabbit with the cat (卯 mǎo → mèo). Korea runs its own meridian too. Since 2017 the calendar itself has had a national standard in China — GB/T 33661-2017 — computed for Chinese Standard Time from modern ephemerides under the Purple Mountain Observatory.

A short history of 102 calendars

Classical texts record 102 official Chinese calendars, each dynasty patching the last. The Taichu calendar of 104 BCE fixed the year at 365 + 385/1539 days and introduced the paired solar terms — the twelve zhōngqì whose job of marking the months survives unchanged. The Shoushi calendar of 1281 (Guo Shoujing, Yuan dynasty) measured the year at 365.2425 days — the value the Gregorian reform would adopt three centuries later. The Shixian calendar of 1645 was compiled under the Jesuit Adam Schall, finishing Xu Guangqi's project with Copernicus, Kepler and Tycho on the shelf — and switched the solar terms to true ecliptic longitude. That is essentially the calendar on this page: Shixian's rules, Beijing time, modern astronomy.

Underneath the machinery, an older machine still runs. The sixty-name day cycle has been counted without one missed step since the eclipses recorded in the Spring and Autumn Annals (722–481 BCE) — two and a half thousand years of unbroken day-counting, checked against those eclipses. The year cycle is younger (it went continuous under the Western Han) and still names eras: 1984 began the current 甲子 jiǎzǐ cycle; 2044 begins the next. A silk manuscript from Mawangdui, sealed in 168 BCE, already used the wheel — it marks Qin Shi Huang's first year, 246 BC, as term 52, 乙卯 yǐmǎo.

Days, hours, ages

Days begin at midnight and carry their own sexagenary name, written with a small numeral grammar: days 1–10 are 初一 through 初十, 11–19 are plain tens, 20 is 二十, 21–29 use 廿 (niàn, a contracted "twenty"), 30 is 三十. Months have no fixed length: each is big (大, 30 days) or small (小, 29), decided fresh by where the new moons land. Before the seven-day week arrived, months were split into three 旬 xún — ten-day weeks whose thirds still name parts of a month in East Asia.

The twelve branches also mark the twelve double-hours: 子 covers 23:00–01:00 and noon sits in 午 (11:00–13:00). And a traditional person is one year old at birth, gaining a year at every New Year — 虛歲, the "nominal age", a completely different number from the western one.

Honest limits

The tables behind this page cover lunisolar years 1901 through 2099 (the next New Year, closing the run, falls on February 9, 2100). They encode the modern published calendar — Shixian rules on Chinese Standard Time — and were checked month-for-month against the Hong Kong Observatory's official Gregorian–Lunar conversion tables. Dates before 1645 followed older calculations and will not agree; dates in other East Asian countries can differ by a day because they use their own meridians; and a "date" here is a whole day, not an instant. Readings for January dates belong to the previous lunisolar year — the zodiac finder handles that for you.