Stage 1 · Term 9 of 34
Sexagenary Cycle 六十甲子
Liù Shí Jiǎ Zǐ
The 60 stem-branch pairs formed by cycling 10 stems against 12 branches, starting with 甲子. Years, months, days and hours each march through this cycle continuously — it is the calendar arithmetic under every chart.
In the classics
The sixty pairs, beginning 甲子 and ending 癸亥, are the oldest layer of the system — used for date records since the oracle-bone era, long before BaZi existed. 《三命通会》 opens its method chapters from this arithmetic, including each pair's nayin (纳音) sound-element.
In a chart
The cycle is the clockwork under everything: years, months, days and double-hours each march through the same sixty pairs at their own speed, which is why a birth moment yields four pairs at once. Only half the mathematically possible combinations occur — yang stems pair only with yang branches, yin with yin — so 甲丑 or 乙子 can never exist, a quick sanity check on any chart you're shown.
Worked example
2026 is a 丙午 year. Sixty years earlier, 1966 was also 丙午 — the same pair returns at every complete revolution, which is why a 60th birthday classically "completes the cycle" (还历).
Where beginners misread it
Assuming the cycle is astronomy. It is pure counting — a modular calendar — and its power in BaZi comes from the relations between pairs, not from any physical claim.
The classical rules here are public; the lineage method for applying them to a specific chart is taught, not read — see Yixin Academy's courses.
learnwithyixin.com/courses →What does Sexagenary Cycle mean in BaZi?
The 60 stem-branch pairs formed by cycling 10 stems against 12 branches, starting with 甲子. Years, months, days and hours each march through this cycle continuously — it is the calendar arithmetic under every chart.