学 · learn · 周易
Heavenly stems and earthly branches
天干地支 — the ten heavenly stems and twelve earthly branches — is the counting system beneath most Chinese timekeeping. Two lists of characters, paired off, and they will not repeat for sixty years.
干
Ten and twelve
The ten stems (甲乙丙丁戊己庚辛壬癸) are paired with the twelve branches (子丑寅卯辰巳午未申酉戌亥). Pair the first of each, then the second of each, and so on.
Because ten and twelve share a factor of two, only sixty combinations exist. That is the sexagenary cycle: it returns to its starting point after sixty steps.
That is where the zodiac comes from
The twelve branches carry the twelve animals — 子 the rat, 丑 the ox, 寅 the tiger, and the rest. So the “year of the …” system is a small window onto the branches, not the whole thing.
The full pair is what a year is called: 甲辰, 乙巳, 丙午 and so on. Each such pairing lasts a year, and returns once in sixty.
It marks days too, not just years
The same cycle labels days. Today's date in the Chinese calendar is written with a stem-branch pair — for example 乙未日 — and traditional almanacs have used that day marker for choosing times and directions for centuries.
An almanac page will also give the hour: two-hour blocks, each with its own branch.
Where it turns up in practice
BaZi reads your birth year, month, day and hour as four stem-branch pairs — eight characters in total, which is exactly what 八字 (“eight characters”) means.
The almanac uses the day pair for its 宜 / 忌 advice. And the sixty-year cycle is why a “complete life cycle” is traditionally celebrated at sixty.
Try it tonight
See the day's stem-branch pair and what tradition reads into it — in plain words.
Open today's almanacQuestions people ask
What does 八字 mean literally?
Eight characters: the stem and branch of your year, month, day and hour. Four pairs, eight characters.
Is the sexagenary cycle a calendar?
It is a counting cycle that calendars use. The same cycle labels years, months, days and hours.
Why sixty?
Ten stems and twelve branches pair in step, and the lowest common multiple of 10 and 12 is 60 — so the pairing repeats every sixty steps.
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Last updated 2 November 2026
An ancient Chinese divination. If today is heavier than words, findahelpline.com lists real helplines near you.