The Calendar: Solar Terms and Chart Calculation
Bazi uses the solar calendar (not the lunar calendar) as its foundational timing system. This is one of the most misunderstood aspects of the system.
Solar Terms (节气)
The Chinese solar year is divided into 24 solar terms — each marking a precise astronomical moment when the sun reaches a specific degree of the ecliptic. These are the actual month boundaries in Bazi:
| Solar Term | Approx. Date | Month in Bazi |
|---|---|---|
| Start of Spring (立春) | Feb 4 | Month 1 |
| Start of Summer (立夏) | May 6 | Month 4 |
| Start of Autumn (立秋) | Aug 7 | Month 7 |
| Start of Winter (立冬) | Nov 7 | Month 10 |
The exact date shifts slightly each year. Bazi software computes the solar terms to the minute — do not rely on fixed dates.
Two Key Boundary Rules
- Month change: The month pillar changes at each solar term, not at the first day of the lunar month.
- Year change: The year pillar changes at Start of Spring (Lì Chūn, around February 4), not at Lunar New Year or January 1.
If you were born in January or early February, your Bazi year may differ from what you expect. Check your chart software carefully.
Birth Hour
The hour pillar uses traditional two-hour divisions. The day begins at 11pm (子时), not midnight. Birth times near the hour boundary require special attention.