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Tong Shu Calendar Reference

Auspicious Business Opening Dates for May 2026開業 · May 2026

By Master Sean Chan · Updated

This month carries Li Xia (立夏) — start of the BaZi summer on May 5 (Singapore time): the BaZi calendar's sectional boundary for the month. Mid-month transition into the BaZi summer; element balance shifts noticeably across the term.Below is the universal Chinese metaphysics ranking of every day in May 2026 for opening a business (開市), derived from the classical Tong Shu (通書). Opening is treated as a 'beginning' — the rules favour 開 (Opening) and 建 (Establishing) officers and Yellow Dao days carrying 天德 / 月德 protection.

Top-ranked dates this month

31
days in May
27
pass hard requirements
6
rank as 上吉
5
top picks below
DateDay PillarOfficer 建除 Mansion 宿Clash 沖Class
12026-05-14辛卯開 Opening軫酉 (Rooster)上吉
22026-05-24辛丑成 Completing女未 (Goat)上吉
32026-05-18乙未滿 Filling房丑 (Ox)上吉
42026-05-09丙戌執 Holding鬼辰 (Dragon)上吉
52026-05-12己丑成 Completing張未 (Goat)上吉

All days in May 2026

DateDay PillarOfficerMansion ClashNotable factorsClass
2026-05-01戊寅開奎申 Monkey建除 開 · 黃道上吉
2026-05-02己卯閉婁酉 Rooster建除 閉凶
2026-05-03庚辰建胃戌 Dog黃道吉
2026-05-04辛巳除昴亥 Pig四絕 · 黃道凶
2026-05-05壬午除畢子 Rat黃道吉
2026-05-06癸未滿觜丑 Ox建除 滿 · 黃道吉
2026-05-07甲申平參寅 Tiger建除 平 · 宿 參平
2026-05-08乙酉定井卯 Rabbit月德合 · 宿 井吉
2026-05-09丙戌執鬼辰 Dragon天德合 · 建除 執 · 黃道上吉
2026-05-10丁亥破柳巳 SnakeFailed requirement: not_month_break大凶
2026-05-11戊子危星午 HorseFailed requirement: not_year_break大凶
2026-05-12己丑成張未 Goat建除 成 · 宿 張 · 黃道上吉
2026-05-13庚寅收翼申 Monkey月德吉
2026-05-14辛卯開軫酉 Rooster天德 · 建除 開 · 宿 軫上吉
2026-05-15壬辰閉角戌 Dog建除 閉 · 黃道凶
2026-05-16癸巳建亢亥 Pig宿 亢平
2026-05-17甲午除氐子 Rat宿 氐 · 黃道平
2026-05-18乙未滿房丑 Ox月德合 · 建除 滿 · 黃道上吉
2026-05-19丙申平心寅 Tiger天德合 · 建除 平吉
2026-05-20丁酉定尾卯 Rabbit—平
2026-05-21戊戌執箕辰 Dragon建除 執 · 宿 箕 · 黃道吉
2026-05-22己亥破斗巳 SnakeFailed requirement: not_month_break大凶
2026-05-23庚子危牛午 HorseFailed requirement: not_year_break大凶
2026-05-24辛丑成女未 Goat天德 · 建除 成 · 黃道上吉
2026-05-25壬寅收虛申 Monkey宿 虛平
2026-05-26癸卯開危酉 Rooster建除 開 · 宿 危吉
2026-05-27甲辰閉室戌 Dog建除 閉 · 黃道凶
2026-05-28乙巳建壁亥 Pig月德合吉
2026-05-29丙午除奎子 Rat天德合 · 黃道吉
2026-05-30丁未滿婁丑 Ox建除 滿 · 黃道吉
2026-05-31戊申平胃寅 Tiger建除 平平
Personalised next step

BaZi-Aligned Date Report — May 2026

USD 388

A personalised PDF that re-ranks every business opening-suitable day in May 2026 against your BaZi (and, for weddings/ROM, your partner’s BaZi). It surfaces:

Order the report →

See the full glossary of classical date-selection terms in the BaZi Glossary & Auxiliary Stars.

Further reading from the blog

Selected posts from Master Sean Chan's blog covering this topic and closely related ones in practice:

Frequently asked

Why isn’t my day on the list of top 5?

The top list is the universal ranking before any personal adjustment. Many couples find their best date isn’t in the top 5. Once you account for your day pillars, the right day often shifts. That’s exactly the gap the BaZi-Aligned Date Report fills.

What does 大凶 mean and can it ever be overridden?

大凶 means the day fails a hard classical requirement: 月破 (month break), 歲破 (year break), or 四離/四絕 (a quarter-day boundary). These cannot be overridden by personal alignment; they are excluded categorically. Choose another day.

Why don’t you show times here?

Hour selection is personal. The right hour depends on your day pillar and the chosen day’s element relationship to it. Publishing universal “auspicious hours” misleads readers into thinking a generic hour is safe; it isn’t. Hours are included in the personalised report.

Where do these scores come from?

The classical Tong Shu (通書) tradition: 建除十二神 (Twelve Officers), 二十八宿 (Twenty-Eight Mansions), 月德 / 天德 (monthly and yearly virtue stars), 黃黑道 (Yellow/Black Dao), and the Dong Gong (董公) per-purpose rules. We compute these directly from astronomical solar terms — no app shortcuts.

Should I open the business on the same day as my company registration?

If you can — yes. Aligning the opening with the legal incorporation compounds the day’s influence on both events. If they have to be different, prioritise the opening (the customer-facing first day) over the registration date.

Methodology

Each day’s pillar is computed from the 60 Jiazi rotation anchored against the published Tong Shu, not from any single calendar app. The BaZi year flips at Li Chun (立春) and the BaZi month flips at every sectional solar term, both calculated from VSOP87 solar-longitude data so the boundaries land on the right minute. Twelve Officers and the 28 Mansions each rotate deterministically against well-known anchors.

The per-purpose weights are Dong Gong’s (董公擇日) — adjusted where modern almanacs disagree, in favour of the Hong Kong Observatory and Taiwan CWB lineage. Auspicious stars add to the score, taboo stars subtract, the day’s officer and mansion shift it further, and Yellow Dao adds a final small bonus. The final number gets capped at 100 and mapped to one of five tiers.