建除十二神 Day Fitness Cycle (Jiàn Chú Shí'èr Shén)

The Day Fitness cycle (建除十二神) is a twelve-day repeating cycle used in traditional Chinese almanacs (通書/黃曆) to classify each day's suitability for various activities. Each of the twelve positions — 建 (Establish), 除 (Remove), 滿 (Full), 平 (Balance), 定 (Stable), 執 (Grasp), 破 (Break), 危 (Danger), 成 (Succeed), 收 (Receive), 開 (Open), 閉 (Close) — carries traditional associations that guide date selection (擇日) for important events.

See also: Almanac Flags · Virtue Stars · Deity Directions

The Cycle

The cycle starts on the day whose branch matches the month branch (建日), then advances through 12 values:

#	Fitness	Meaning	Auspicious
1	建	Establishing	Yes
2	除	Removing	Yes
3	滿	Fullness	Yes
4	平	Leveling	No
5	定	Settling	Yes
6	執	Grasping	No
7	破	Breaking	No
8	危	Danger	No
9	成	Completion	Yes
10	收	Collecting	No
11	開	Opening	Yes
12	閉	Closing	No

Six auspicious (吉): 建, 除, 滿, 定, 成, 開

Six inauspicious (凶): 平, 執, 破, 危, 收, 閉

Determination Rule

offset = (dayBranchIndex - monthBranchIndex) mod 12
fitness = DAY_FITNESS_CYCLE[offset]

The month branch is determined by solar month boundaries (節氣), the same as the month pillar in 四柱.

Example: If the month branch is 寅 (index 2) and the day branch is 辰 (index 4):

• offset = (4 - 2) mod 12 = 2
• fitness = 滿 (fullness, auspicious)

API

import { getDayFitness, getDayFitnessForDate } from 'stem-branch';

// From branches directly
getDayFitness('辰', '寅'); // → '滿'

// From a date (computes pillars automatically)
getDayFitnessForDate(new Date(2024, 5, 15));
// → { fitness: '成', auspicious: true }

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See Also

• 神煞 Almanac Flags — 30 symbolic markers for BaZi and date selection
• 天德月德 Virtue Stars — Monthly auspicious stars (Heavenly and Monthly Virtue)
• 神煞方位 Deity Directions — Daily compass directions for four deities