How the Daily Hexagram Is Calculated

The method

Each day, three numbers derived from the Chinese calendar are summed and reduced to pick a trigram pair — the same procedure used for centuries to cast a hexagram from a date rather than a coin toss or yarrow stalks:

• Year branch number (yb) — the Earthly Branch of the BaZi year pillar, numbered 子=1 … 亥=12.
• Lunar month (lm) — 1–12 (leap months use the base month number, without a leap offset — standard Meihua convention).
• Lunar day (ld) — 1–30.

S = yb + lm + ld
Upper trigram (上卦) = S mod 8 (a remainder of 0 means 8)
Lower trigram (下卦) = (S + 1) mod 8 — the +1 represents the 子 (midnight) hour, fixed because the hexagram is cast at the day boundary, consistent with our almanac's night-zi (夜子时) convention
Changing line (动爻) = (S + 1) mod 6, counted from the bottom (line 1) — a remainder of 0 means line 6

Worked example — today, 2026-08-11

Trigram numbers used above are Earlier-Heaven (先天数): 1 乾 · 2 兑 · 3 离 · 4 震 · 5 巽 · 6 坎 · 7 艮 · 8 坤.

Sourcing, honestly

The derivation method comes from 《梅花易数》(Meihua Yishu). It is traditionally attributed to the Song-dynasty scholar Shao Yong (邵雍) — 旧题邵雍，实为后世辑成: in fact, textual scholarship dates the compilation to the Ming era, centuries after Shao Yong's lifetime. We say so plainly rather than repeat the traditional attribution as settled fact. What the method offers is not a famous author's endorsement but a long, consistent tradition of casting a hexagram from a date.

The hexagram corpus itself (name, judgment, koan) is verified against the received text (通行本), the Ten Wings, and the orthodox 程朱 commentary tradition (王弼, 程颐, 朱熹), cross-checked against Wilhelm–Baynes and Lynn for the English. Full bibliography available on request.