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Tong Shu Calendar Reference

Auspicious Business Opening Dates for May 2027開業 · May 2027

By Master Sean Chan · Updated

This month carries Li Xia (立夏) — start of the BaZi summer on May 6 (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 2027 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
24
pass hard requirements
4
rank as 上吉
5
top picks below
DateDay PillarOfficer 建除 Mansion 宿Clash 沖Class
12027-05-09辛卯Opening酉 (Rooster)上吉
22027-05-13乙未滿 Filling丑 (Ox)上吉
32027-05-28庚戌Holding辰 (Dragon)上吉
42027-05-21癸卯Opening酉 (Rooster)上吉
52027-05-08庚寅Gathering申 (Monkey)

All days in May 2027

DateDay PillarOfficerMansion ClashNotable factorsClass
2027-05-01癸未丑 Ox建除 平
2027-05-02甲申寅 Tiger黃道
2027-05-03乙酉卯 Rabbit建除 執 · 黃道
2027-05-04丙戌辰 DragonFailed requirement: not_month_break大凶
2027-05-05丁亥巳 SnakeFailed requirement: not_month_break大凶
2027-05-06戊子午 Horse建除 危 · 宿 參
2027-05-07己丑未 GoatFailed requirement: not_year_break大凶
2027-05-08庚寅申 Monkey月德
2027-05-09辛卯酉 Rooster天德 · 建除 開上吉
2027-05-10壬辰戌 Dog建除 閉 · 黃道
2027-05-11癸巳亥 Pig宿 張
2027-05-12甲午子 Rat黃道
2027-05-13乙未滿丑 Ox月德合 · 建除 滿 · 宿 軫上吉
2027-05-14丙申寅 Tiger天德合 · 建除 平
2027-05-15丁酉卯 Rabbit宿 亢
2027-05-16戊戌辰 Dragon建除 執 · 宿 氐 · 黃道
2027-05-17己亥巳 SnakeFailed requirement: not_month_break大凶
2027-05-18庚子午 Horse月德 · 建除 危
2027-05-19辛丑未 GoatFailed requirement: not_year_break大凶
2027-05-20壬寅申 Monkey宿 箕
2027-05-21癸卯酉 Rooster建除 開 · 宿 斗上吉
2027-05-22甲辰戌 Dog建除 閉 · 黃道
2027-05-23乙巳亥 Pig月德合
2027-05-24丙午子 Rat天德合 · 宿 虛 · 黃道
2027-05-25丁未滿丑 Ox建除 滿 · 宿 危 · 黃道
2027-05-26戊申寅 Tiger建除 平
2027-05-27己酉卯 Rabbit
2027-05-28庚戌辰 Dragon月德 · 建除 執 · 黃道上吉
2027-05-29辛亥巳 SnakeFailed requirement: not_month_break大凶
2027-05-30壬子午 Horse建除 危
2027-05-31癸丑未 GoatFailed requirement: not_year_break大凶
Personalised next step

BaZi-Aligned Date Report — May 2027

USD 388

A personalised PDF that re-ranks every business opening-suitable day in May 2027 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.