BaZi Calculator

The commonest disagreement is the year pillar. The BaZi year is a solar year beginning at Lichun — the moment the Sun reaches 315° of apparent ecliptic longitude. Chinese New Year is a product of the lunar month, and the two sit anywhere from a few days to a month apart, in either order depending on the year. A calculator that splits the year at New Year gives everyone born between the two dates a year pillar that is off by a whole cycle, which then changes every Ten God, the element balance, and the luck pillars.

The second is the month pillar. It changes only at the instant of one of the twelve Jie, and each of those instants drifts across the day from year to year. Treating a solar term as a fixed calendar date guarantees a wrong month pillar for anyone born on those twelve high-risk days each year.

The third is the hour pillar, and it is the one most often skipped. Classical practice reads the hour from where the Sun actually is, which is true solar time. The gap to clock time has two parts: the longitude difference from the timezone's central meridian (about 4 minutes per degree), and the equation of time, which swings within ±16 minutes across the year from the Earth's orbital eccentricity and axial tilt. China runs a single UTC+8 clock across roughly 60° of longitude, so a birth in Ürümqi is read almost two hours away from the clock on the wall.

The Zi hour has no single right answer — and there are three positions, not two. For 23:00–24:00: one school advances both the day pillar and the hour stem into the next day; another keeps the whole hour on the current day; a third keeps the day pillar where it is but takes the hour stem from the next day, treating the Zi hour as one span across midnight anchored to the day it ends in. All three have classical support and they differ by a whole day pillar. This site computes all three and labels which is active, defaulting to the third — it is what lunar-javascript produces by default, and therefore what most Chinese calculators show.