Lunar Calendar & Solar Terms

How the Chinese calendar works and why it matters for Bazi

Lunisolar, Not Purely Lunar

The Chinese calendar is lunisolar — it tracks both moon phases (months) and the solar year (seasons). Each month begins with a new moon, making months 29-30 days. But 12 lunar months total about 354 days — roughly 11 days shorter than a solar year. To stay in sync with the seasons, a leap month (闰月) is inserted approximately every 3 years.

The 24 Solar Terms (节气)

The year is divided into 24 solar terms, spaced approximately 15 days apart, based on the sun's position. These terms have poetic names reflecting seasonal changes: Beginning of Spring (立春), Rain Water (雨水), Awakening of Insects (惊蛰), Spring Equinox (春分), Clear and Bright (清明), Grain Rain (谷雨), and so on through all four seasons. Each term represents a specific climatic moment that guided agricultural life for millennia.

Why Solar Terms Matter for Bazi

This is critical: the Bazi Month Pillar does NOT change on the 1st of the lunar month. It changes at the Solar Term. For example, the Yin (Tiger) month — the first month of the Bazi year — begins at 立春 (Beginning of Spring, around February 4), not on Chinese New Year. Someone born on February 3 might have the previous year's Bazi chart, while someone born February 5 is in the new year. Always use a reliable calendar converter for birth dates near month boundaries.

Practical Tips for Birth Dates

1. If you were born near the beginning or end of a solar term (typically around the 4th-8th or 19th-23rd of a month), double-check your Bazi month pillar. 2. The Bazi day changes at midnight local time, but the Bazi hour follows the 12 shichen (2-hour blocks starting at 23:00). 3. For births outside China, convert to local solar time (not timezone) for the most accurate Bazi calculation. 4. When in doubt, use the Bazi calculator in this app — it handles all these conversions automatically.