Four Pillars, calculated with the math you've been promised.
Your year, month, day, and hour stems and branches — computed with the lichun year boundary, optional true solar time correction, and transparent zi-hour school selection. Hidden stems (藏干) included.
Your birth details
Computed in your browser. Your birth data never leaves this device.
Gender
Used only to determine luck-pillar direction (阳男阴女顺行). We make no assumptions about your identity.
i.
What the Four Pillars are
Ba Zi (八字), literally "eight characters," is the most architecturally precise system in the Chinese astrological tradition. Each of the eight characters is one heavenly stem (天干) or earthly branch (地支), paired across four pillars: year, month, day, and hour of birth. The day pillar's heavenly stem—your Day Master—is the single most important character in the chart. It represents your core self.
Unlike the Western zodiac, which sorts everyone into twelve archetypes by sun sign alone, the Four Pillars sorts into 60 day masters (the sexagenary cycle) and further differentiates by the surrounding seven characters. The combinatorial space is roughly 518,400 — larger than the number of distinct charts a single human population can fill in a lifetime.
ii.
How we calculate it
We follow the academic consensus on every fork in the algorithm. The year pillar changes at lichun (立春) — the solar-term beginning of spring — not at the Chinese New Year. The day pillar follows the sexagenary cycle uninterrupted across centuries. The hour pillar uses two-hour blocks named for the earthly branches.
For births near a time-zone boundary, we offer optional true solar time correction. This applies a longitude-based offset plus the equation of time (a seasonal correction of up to ±16 minutes). Most calculators silently skip this step. We surface it because the choice changes your hour pillar.
The zi hour (子时, 23:00–01:00) has been debated for centuries. We default to the split-zi (分子) school: day pillar stays on the previous day, but the hour stem is computed from the next day's stem via the 五鼠遁 rule. You can switch to early-zi in advanced options. Full sources are documented on the methodology page.
iii.
What we do not do
We do not tell you that your chart is "broken." We do not predict specific diseases or wedding dates. We do not sell rituals to "cure" elements you are missing. Classical BaZi — the version preserved in the San Ming Tong Hui (三命通会) and Di Tian Sui (滴天髓) — is a system for understanding patterns, not a verdict machine.