How the charts are calculated

Calculated, then interpreted

Two different things happen when you read a chart here. First, a calculation: from your birth date, time and place we derive the BaZi four pillars, the Zi Wei Dou Shu star map and, for a question, a Qi Men board. These are deterministic — the same inputs always give the same chart, and you can check them against any published almanac.

Then an interpretation: what those patterns have traditionally been taken to mean. The Classic lens stays close to the classical vocabulary; the Inner Constellation tells the same chart as a story in plain words. Both are readings of the same calculation. Where a page shows a calculated fact, it is labelled Calculated; everything else is interpretation.

Birth time and place

• The pillars use the local time at your birth place on that date, including historical rules — Singapore before 1982 used UTC+7:30, for example — resolved from the city you pick.
• True solar time is optional: when ticked, we shift the clock time by your birth place’s longitude so the hour pillar follows the sun rather than the time zone.
• If you don’t know your birth time, we read the year, month and day. The hour pillar and the Zi Wei star map need a time, so those parts stay quiet rather than guess.
• Birth times near a two-hour boundary (for example 23:00 or 01:00) can fall in either hour pillar depending on convention; if yours is close, try both.

BaZi 八字 — the four pillars

• Months are divided at the solar terms (節氣), not at the lunar month — the classical convention for BaZi. Years change at 立春 (around 4 February), not at Lunar New Year.
• The Day Master (日主) is the Heavenly Stem of the day pillar. Every Ten God (十神) label compares another stem’s element and polarity with it.
• Each Earthly Branch carries hidden stems (藏干), listed main qi first. Sub-stars are their Ten Gods against the Day Master.
• The ten-year luck pillars (大運) step forward or backward from the month pillar according to the year stem’s polarity and the sex at birth. The start age counts days from birth to the nearest solar term, three days to a year. Our count is day-precise, without the birth-hour refinement, so it can differ by a few months from an hour-precise almanac.
• The element balance counts the main qi of each stem and branch, plus today’s. It shows what is abundant and what is scarce in the chart; it is not a verdict on whether the Day Master is strong or weak, which needs a fuller weighing of season, roots and support.
• Branch relationships implemented: six combinations (六合), six clashes (六沖), six harms (六害) and the three-harmony frames (三合). Punishments (三刑) and destructions (相破) are not yet included.

Zi Wei Dou Shu 紫微斗數 — the star map

• The star map is plotted from the lunar calendar date and the birth hour, as the tradition requires, with the twelve palaces placed from the life palace.
• We use the open-source iztro library’s standard conventions, including the four transformations (四化) by year stem and the decade (大限), annual (流年), monthly and daily flows.
• Schools differ on some points — the placement of a few assistant stars, and how brightness is graded. Where our chart disagrees with another reader’s, the difference is usually one of these conventions rather than an error.

Qi Men Dun Jia 奇門遁甲 — the strategy board

• A Qi Men board is cast for the moment a question is asked, not from your birth chart. The one shown on your chart page is today’s board at the time you opened it.
• We use the 時家奇門 hour method: the governing solar term sets the 局, and the 上/中/下元 is fixed by the 符頭 rule (the 超神接氣 convention). Schools that use 拆補 or 置閏, or flying-palace methods, will show a different board for some hours.
• Qi Men readings describe the quality of a moment for a kind of action. They are kept separate from the natal readings on purpose.

Where the AI comes in

The free chart, the chart sheet, the element balance, the luck pillars and the written “no-AI” readings are all rule-based and run in your browser. Nothing is sent anywhere unless you choose to save or share.

The Daily Season reading and Ask the Sky (Sky & Season Plus) use an AI model. It receives the calculated chart facts — pillars, stars, Ten Gods, today’s pillars — never your name, email or contact details, and it is instructed to treat those facts as evidence it must not contradict. Every Inner Constellation reading is checked for classical jargon before it reaches you.

What a reading can and cannot tell you

A chart describes tendencies and timing: what tends to come easily, what tends to take effort, and which windows sit more comfortably with your pattern. It does not predict events, and nothing here should replace medical, legal or financial advice. We say this on every reading because we mean it.

Found a calculation you believe is wrong? Write to hello@skyandseason.com with the birth details and the almanac you compared against — we check every report.

About our approach