Year animal and Four Pillars, boundaries stated
BaZi, the Four Pillars, reads a birth moment as four stem-and-branch pairs: year, month, day and hour. This calculator computes all four from documented calendar algorithms, and it is explicit about the two conventions that decide edge cases. The year and month pillars follow the solar calendar of the tradition, turning at Lichun (about 4 February) and at the solar terms, not at Lunar New Year; a birth in the January-February window is flagged, because under the lunar convention the animal can differ. Birth time is read as the local clock time you enter; enter the hour if you know it, and the page states plainly which pillars a missing or boundary time affects. The tradition’s readings are cultural interpretation, presented as entertainment; the pillars themselves are exact calendar arithmetic.
Disclaimer: This calculator gives estimates for general information only. It is not financial, medical or other professional advice. Chinese zodiac and BaZi readings are cultural tradition presented for entertainment; they are not scientific predictions, and solar-term dates near a boundary can differ by a day in a given year, as the results flag.
What this calculator does
It computes the sexagenary (60-cycle) pillars of a birth date and time. The Year pillar comes from the cycle year, which for BaZi begins at Lichun, the solar term near 4 February: births before it belong to the previous cycle year, and the animal shown is that cycle year’s branch. The Month pillar follows the solar terms, each month beginning at a term (Lichun, Jingzhe, Qingming and so on, on their standard dates), with its stem derived from the year stem by the traditional rule. The Day pillar counts days through the unbroken 60-day cycle from a documented anchor date. The Hour pillar takes its branch from the two-hour period of the birth time and its stem from the day stem by the traditional rule. An element tally of the pillars’ stems and branches is shown as a simple surface count, labelled as such, because the full traditional weighting (which counts hidden stems inside branches) is a deeper exercise this page does not pretend to finish.
How to use it
- January and February births: read the flag. If your birthday falls before Lichun, the BaZi year is the previous one, and if it falls between Lunar New Year and Lichun in a year when the festival came first, the popular (lunar) animal and the BaZi animal genuinely differ. Neither is a mistake; they are different conventions, and the results state which one you are looking at.
- Birth time quality controls the Hour pillar only. A rounded or family-recalled time near a two-hour boundary (especially 23:00, where some schools roll the day pillar forward) can flip the hour branch, and the page flags times within 15 minutes of a boundary. The other three pillars do not depend on the hour at all.
- Times are local, as recorded. Traditional practice uses the local solar time of the birthplace, and some schools correct clock time for longitude and the equation of time. This page takes the recorded local time at face value and says so; births near a boundary are the cases where a practitioner’s correction could matter.
- Dates near a solar term can be off by a day. Term dates in the table used here are the standard published dates; in a given year a term can fall a day earlier or later. A birth on a term’s date itself is flagged to check that year’s almanac if the month pillar is critical.
- The animal is the branch of the year. When you only want the zodiac animal, the headline is your answer, with the Lichun caveat for early-year births. The element beside it (from the year stem) is why 1990 is not just Horse but Metal Horse, and the pair repeats only every 60 years.
How it is calculated
- Stems and branches: 10 Heavenly Stems (Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui, cycling through Wood, Fire, Earth, Metal, Water in yin and yang) and 12 Earthly Branches (Zi Rat, Chou Ox, Yin Tiger, Mao Rabbit, Chen Dragon, Si Snake, Wu Horse, Wei Goat, Shen Monkey, You Rooster, Xu Dog, Hai Pig) combine into the 60-pair sexagenary cycle. For cycle year Y: stem = (Y – 4) mod 10, branch = (Y – 4) mod 12.
- Month stems (the “five tigers” rule): the Yin (tiger) month starting at Lichun takes stem Bing for Jia and Ji years, Wu for Yi and Geng years, Geng for Bing and Xin years, Ren for Ding and Ren years, Jia for Wu and Gui years; stems then advance month by month. Month boundaries are the solar terms on their standard dates (Lichun Feb 4, Jingzhe Mar 6, Qingming Apr 5, Lixia May 6, Mangzhong Jun 6, Xiaoshu Jul 7, Liqiu Aug 8, Bailu Sep 8, Hanlu Oct 8, Lidong Nov 7, Daxue Dec 7, Xiaohan Jan 6).
- Day pillar: days are counted from the anchor 1 October 1949, a Jia-Zi day in the published almanacs, through the continuous 60-day cycle (day index mod 60; the same formula reproduces, for example, 10 February 2024 as Jia-Chen). Hour stems (the “five rats” rule): the Zi hour takes stem Jia for Jia and Ji days, Bing for Yi and Geng days, Wu for Bing and Xin days, Geng for Ding and Ren days, Ren for Wu and Gui days; stems advance hour by hour through the branches.
Worked examples
A full chart: 17 May 1990, 10:30. Year: after Lichun, cycle year 1990 gives Geng-Wu, Metal Horse. Month: 17 May falls after Lixia (6 May), the Si month; a Geng year starts its months at Wu-Yin, advancing to Xin-Si by the Si month. Day: the cycle count lands on Ren-Wu. Hour: 10:30 is the Si hour; a Ren day starts its hours at Geng-Zi, advancing to Yi-Si at Si. Four pillars: Geng-Wu, Xin-Si, Ren-Wu, Yi-Si, and the surface element count reads Metal 2, Fire 4, Water 1, Wood 1, Earth 0.
The boundary case: 3 February 1990. One day before Lichun, so the cycle year is still 1989: Ji-Si, Earth Snake, not the Horse of 1990. Under the lunar convention the answer for that date depends on when Lunar New Year fell (26 January in 1990, so the lunar reading also gives Snake here, by its own route). The flag in the results exists for birthdays in this window every year, because in years when the festival falls after Lichun, or the gap runs the other way, the two conventions part company and a single unlabelled answer would be wrong under one of them.
Reading your results
Read the pillars as the chart’s data and the animal as its headline. In the tradition, the Day stem (the first character of the third pillar) is taken as the self element, and readings proceed from its relations to the other pillars; the short traditional notes beside the results gesture at that without performing a full reading, which depends on hidden stems, ten-god relations and luck cycles beyond a calculator’s honest scope. Read the element tally as a surface census only. And read every flag: they mark the exact places (early-February births, term-day births, near-midnight times) where professional practice itself double-checks the almanac.
Limitations
- Solar-term dates are the standard table, ±1 day. Astronomy moves terms by hours year to year; the month (and at Lichun, year) pillar for a birth on a term date may belong to the adjacent month in an exact almanac. The page flags term-day births rather than hiding the uncertainty.
- No longitude or equation-of-time correction. Recorded clock time is used. Strict traditional practice converts to local solar time, which can move a birth across an hour boundary in the far east or west of a time zone; the boundary flag is where this matters.
- The day pillar’s anchor is the published cycle. The 60-day cycle is unbroken in the almanac tradition and the formula is stated so anyone can test it against a known date; calendar reforms before the 20th century and dates outside the supported range of a modern almanac are out of scope.
- Interpretation is cultural, not predictive. BaZi readings are a traditional interpretive art. This page computes the chart, the part that is arithmetic, and offers only brief traditional framing; it makes no claims about character, fate, compatibility or the future, and none should be taken from it.
Frequently asked questions
Why is my Chinese zodiac animal different from what I expected?
Almost always the boundary: the popular animal changes at Lunar New Year, while the BaZi year changes at Lichun (about 4 February), and the two dates rarely coincide. A birth between them belongs to different cycle years under the two conventions. This calculator follows the BaZi (Lichun) convention for its pillars and headline, flags every January-February birth, and explains the other convention beside the result, so the animal you expected is accounted for rather than contradicted.
What are the Four Pillars in BaZi?
Four stem-branch pairs encoding the year, month, day and hour of birth, computed from the sexagenary cycle and the solar calendar: the year by the Lichun-to-Lichun cycle year, the month by the solar terms with its stem ruled by the year stem, the day by the continuous 60-day count, and the hour by the two-hour branch with its stem ruled by the day stem. Together they are the chart a BaZi reading interprets; this page’s worked example (Geng-Wu, Xin-Si, Ren-Wu, Yi-Si for 17 May 1990 at 10:30) shows each pillar’s derivation in turn.
Do I need my birth time?
Only for the Hour pillar. Without it the year, month and day pillars are complete and are what most casual readings use; with it, the chart is complete in the tradition’s terms. Time quality matters more than time precision: a time confidently known to the nearest hour usually fixes the hour branch, while a guess near a boundary may not, which is why near-boundary times are flagged rather than silently resolved.
How often does a full pillar set repeat?
The year pair repeats every 60 years, the day pair every 60 days, and the full four-pillar combination effectively never within a human span of records, which is why the system treats each chart as individual. The sexagenary structure is pure modular arithmetic (stems mod 10, branches mod 12, realigning every 60), and every formula this calculator uses is printed in its method section for checking.
Related calculators
Method: sexagenary cycle arithmetic as defined on this page (Lichun year boundary, solar-term months by the standard date table, day count from the 1 October 1949 Jia-Zi anchor, five-tigers and five-rats stem rules). Readings are cultural tradition for entertainment. Last reviewed: 13 October 2026.