Chinese zodiac

year % 12 is wrong for six weeks every year

Almost every zodiac chart on the internet lists animals against Gregorian years. That is right for about eleven months and wrong for the rest, because the animal changes at Lunar New Year, not on 1 January.

Lunar New Year falls anywhere from 21 January to 20 February. So if you were born between 1 January and Lunar New Year, your animal is the previous year’s:

The last two rows are the point: 31 January and 25 January are on opposite sides of the boundary in different years, so there is no rule of thumb — the date has to be looked up. Enter your birthday above and the tool looks it up.

The second boundary, which almost nobody mentions

There are two conventions, and they disagree for a few weeks most years:

• From 春節 (Lunar New Year). Everyday usage. What you tell people, what a birth announcement says, what the papercut on the window means.
• From 立春. Used by 八字 (BaZi) and 紫微斗數. 立春 is a solar term — the Sun at 315° of ecliptic longitude — and falls on 3, 4 or 5 February every single year.

Across 1900–2100, 立春 comes before Lunar New Year in 103 years out of 200 and after it in the other 97, so which convention you use genuinely changes the answer for anyone born in that window. In 1985 they were sixteen days apart.

The tool shows both, and only tells you they differ when they actually do. Neither is a mistake; they are answers to different questions. If a fortune teller has given you a different animal from the one your family uses, this is why.

生肖 is the small half of a bigger cycle

The twelve animals are the earthly branches (地支). Alongside them run ten heavenly stems (天干), and the two turn together: 甲子, 乙丑, 丙寅, and so on. Because 10 and 12 have a common factor of 2, the pair repeats every 60 years, not every 120.

So a year is not “the dragon year” — it is 甲辰, the wood dragon, and the next wood dragon is sixty years away in 2084. The five elements come from the stems in pairs: 甲乙 wood, 丙丁 fire, 戊己 earth, 庚辛 metal, 壬癸 water.

That sixtieth birthday matters: 花甲, the completion of one full cycle, when your stem-branch year comes round again for the first time since you were born. It is not a metaphor for old age, it is an exact count.

Rat, ox, tiger — and why the ordering is not zoological

The order 鼠牛虎兔龍蛇馬羊猴雞狗豬 is fixed and has nothing to do with size, speed or importance. It is the branch order, which is far older than the animals attached to it: the twelve branches were a counting system for years, months, days and double-hours before they picked up a menagerie. 子時 is 23:00–01:00, and the rat came later.

Which is also why the animals vary between cultures that borrowed the branches. Vietnam has a cat where China has a rabbit; Japan has a boar where China has a pig. The branch 卯 and 亥 did not change.

What this uses

A lunar calendar table generated at build time from astronomical computation and checked against published Lunar New Year dates before it is allowed to ship. It covers 1900 to 2100, and refuses rather than extrapolates outside that.

Everything runs in your browser. For the full date conversion see the lunar calendar converter; for the whole 節氣 year, the 24 solar terms.