The chart is calculated,
not generated.

The calendar underneath

Pillars are drawn from the classical Chinese calendar (만세력 / 万年暦), using astronomical solar terms rather than calendar months. Your month pillar changes at the solar term, not on the first of the month — so someone born on 4 February may belong to the previous month's pillar.

For the year and month pillars, the birth instant is converted to the Asia/Shanghai reference clock before the solar-term boundary is evaluated. This matters most for births close to a term boundary.

True solar time

True solar time is an optional experimental correction and is off by default. When it is off, the chart uses the recorded civil clock time without this adjustment.

When you choose to turn it on, we correct for two things: the gap between longitude and the centre of the timezone, and the equation of time — the yearly wobble caused by the Earth's tilted, elliptical orbit.

We do not ask for your exact birthplace, so the longitude used is a representative one for the timezone you select — Asia/Seoul is read at Seoul's longitude. A birth elsewhere in the same timezone carries an error of a few minutes: Busan differs from Seoul by about 8 minutes of solar time.

For Seoul under UTC+9, the longitude part is about −32 minutes. The equation of time is not a fixed ±4 minutes: in our astronomical approximation it varies through the year by roughly −14 to +16 minutes, so the combined correction changes with the birth date.

If you opt in, be aware of what the approximation can move. Near an hour or midnight boundary it may change the hour pillar or move the local solar date into the previous day, changing the day pillar and Day Master. The result records whether the option was actually applied and the minutes used.

Where the day begins

This is the single most contested rule in the tradition, so we state our choice plainly: the 子 (Rat) hour begins at 23:00, but the day pillar changes at midnight.

That means a birth at 23:30 is in the 子 hour while retaining the current civil day's day pillar. Other schools roll the day pillar over at 23:00 instead. Neither is 'wrong' — they are different lineages, and a chart calculated under the other convention will differ from ours for births between 23:00 and midnight.

Luck cycles

Luck pillars (대운 / 大運) run forward or backward depending on the polarity of your year stem and your sex — forward for yang-male and yin-female, backward otherwise. The starting age comes from the distance to the neighbouring solar term, at the traditional three-days-to-one-year ratio.

Annual pillars (세운 / 歳運) are then read against your Day Master, and the year-ahead reading breaks the year into twelve solar-term months rather than calendar months.

How the elements are weighted

The displayed element balance gives each visible stem and branch a weight of 2 and each hidden stem a weight of 1. Seasonal support is not added to those percentages. Ten Gods are derived for the other visible stems and the hidden stems from their element and polarity relationship to the Day Master.

A separate beta support heuristic adds peer/resource weight, seasonal support, and roots found in branches, then labels the Day Master support-light, balanced, or support-heavy. The two least represented elements are shown only as balancing candidates, not as a definitive governing-element verdict.

How phone numbers are ranked

For Korean and Japanese mobile formats, we read the four-digit block a customer commonly chooses; for other formats, we use the last four digits. Digits 1–2 map to Wood, 3–4 to Fire, 5–6 to Earth, 7–8 to Metal, and 9–0 to Water.

The chart's Day-Master support label determines which elements are welcomed or already excessive. Each candidate starts at 50: element fit, adjacent generating or controlling flow, and element concentration each add or subtract weighted points. The result is clamped to 6–96, and ties favor a broader element spread and smoother flow. This is a transparent beta ranking for reflection, not a claim that a number causes events.