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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辛卯開 Opening柳酉 (Rooster)上吉
22027-05-13乙未滿 Filling軫丑 (Ox)上吉
32027-05-28庚戌執 Holding奎辰 (Dragon)上吉
42027-05-21癸卯開 Opening斗酉 (Rooster)上吉
52027-05-08庚寅收 Gathering鬼申 (Monkey)吉

All days in May 2027

DateDay PillarOfficerMansion ClashNotable factorsClass
2027-05-01癸未平婁丑 Ox建除 平平
2027-05-02甲申定胃寅 Tiger黃道吉
2027-05-03乙酉執昴卯 Rabbit建除 執 · 黃道吉
2027-05-04丙戌破畢辰 DragonFailed requirement: not_month_break大凶
2027-05-05丁亥破觜巳 SnakeFailed requirement: not_month_break大凶
2027-05-06戊子危參午 Horse建除 危 · 宿 參平
2027-05-07己丑成井未 GoatFailed requirement: not_year_break大凶
2027-05-08庚寅收鬼申 Monkey月德吉
2027-05-09辛卯開柳酉 Rooster天德 · 建除 開上吉
2027-05-10壬辰閉星戌 Dog建除 閉 · 黃道凶
2027-05-11癸巳建張亥 Pig宿 張吉
2027-05-12甲午除翼子 Rat黃道吉
2027-05-13乙未滿軫丑 Ox月德合 · 建除 滿 · 宿 軫上吉
2027-05-14丙申平角寅 Tiger天德合 · 建除 平吉
2027-05-15丁酉定亢卯 Rabbit宿 亢平
2027-05-16戊戌執氐辰 Dragon建除 執 · 宿 氐 · 黃道吉
2027-05-17己亥破房巳 SnakeFailed requirement: not_month_break大凶
2027-05-18庚子危心午 Horse月德 · 建除 危吉
2027-05-19辛丑成尾未 GoatFailed requirement: not_year_break大凶
2027-05-20壬寅收箕申 Monkey宿 箕吉
2027-05-21癸卯開斗酉 Rooster建除 開 · 宿 斗上吉
2027-05-22甲辰閉牛戌 Dog建除 閉 · 黃道凶
2027-05-23乙巳建女亥 Pig月德合吉
2027-05-24丙午除虛子 Rat天德合 · 宿 虛 · 黃道吉
2027-05-25丁未滿危丑 Ox建除 滿 · 宿 危 · 黃道吉
2027-05-26戊申平室寅 Tiger建除 平平
2027-05-27己酉定壁卯 Rabbit—平
2027-05-28庚戌執奎辰 Dragon月德 · 建除 執 · 黃道上吉
2027-05-29辛亥破婁巳 SnakeFailed requirement: not_month_break大凶
2027-05-30壬子危胃午 Horse建除 危平
2027-05-31癸丑成昴未 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.