Four Pillars

What it is

Four Pillars of Destiny — 사주팔자 in Korean, Bazi (八字, "eight characters") in Chinese — converts a birth date and time into four pillars: year, month, day, and hour. Each pillar is a pair of one heavenly stem and one earthly branch, so the whole chart is eight characters in total. The pillars come from the traditional lunar/solar calendar, not the plain Gregorian date, which is why the conversion needs a real calendar engine rather than simple arithmetic on the year, month, and day you were born.

The four pillars are read together, not separately: the day pillar's stem (your day master) is the reference point, and the other three pillars are scored against it through the ten gods and the five-element cycle.

Worked example

For a birth date of August 5, 1990, the year pillar is 庚午, the month pillar 癸未 (adjusted to the solar-term month boundary, not the calendar month), and the day pillar 壬寅 — all three fixed by the date alone, regardless of birth time. Only the hour pillar moves with the clock: at 12:00 noon it is 丙午; move the birth time forward to 1:00 PM — the next two-hour block — and it becomes 丁未. Since the hour pillar's stem changes, the ten-god theme attached to it changes too (see ten gods) — which is why an unknown birth time still leaves you with a real, usable chart, just a less complete one.

How Mystica computes it

The free reading at Saju computes all four pillars from your birth date and time using the lunar-javascript calendar library, the same kind of astronomical calendar-conversion engine professional Saju readers use — not a simplified approximation. If you don't know your birth hour, the reading does not guess one: it shows the hour pillar as "—" with the label "(hour unknown — not interpreted)," and works from the three pillars your date fixes — year, month and day. Nothing from the missing hour pillar is counted in the five-element balance or the ten-god themes, so the chart is less complete, never filled in with a made-up hour.