The Four Pillars
四柱八字

The Four Pillars encode your birth moment as four pairs of a Heavenly Stem (天干 / 천간) and an Earthly Branch (地支 / 지지) — one pair each for the year, month, day and hour.

Solar terms, not the calendar

Bazi years and months follow the sun, not the Gregorian or lunar calendar. The year turns at 立春 (Lichun, ~Feb 4) and each month begins at one of the 12 sectional solar terms. This app computes the sun's apparent ecliptic longitude directly (Meeus' algorithm), so the boundaries are astronomically placed rather than approximated.

True solar time & your longitude

The hour pillar uses true solar time at your birthplace — your clock time corrected for how far your longitude sits from your time-zone meridian, plus the equation of time. This is why location matters, and why the longitude field is there.

Please verify

• Time zone & DST. The UTC-offset field defaults to a city's standard offset. If you were born during daylight saving, or in a year/country whose offset differed, set it yourself. This is the most common source of a wrong hour pillar.
• Births near a boundary. Within a few minutes of a solar term or of midnight / 23:00, small timing errors can shift a pillar. Confirm against a second source if you're on an edge.
• Day-change convention. Schools differ on whether the day flips at 23:00 or midnight. Toggle it in Advanced.