Chinese New Year (Zhengyue Chuyi) 正月初一 Glossary
The first day of the first lunar month — the civil new year of the Chinese calendar, and the year boundary used by folk almanacs and some lineage practice.
Zhēngyuè chūyī · 正月初一 (simplified) · 正月初一 (traditional)
Source credibility (S/A/B/C/X): S A Rule computability (A/B/C): A
What it is
The Chinese calendar is lunisolar: months begin at each new moon, and the first day of the first month （正月初一） is what most people call Chinese New Year — the date of the family dinner, the public holiday, and the popular zodiac changeover. As a calendar fact it is computable to the day: the month start is fixed by the new-moon instant under the national standard's rules (true new-moon month starts, intercalation by the no-major-solar-term rule with the two-winter-solstice check).
But as a year-pillar boundary it is a convention, not a law of the system. Folk almanacs （通書） and some lineage practice treat the civil new year as the point where the year stem-branch changes; Zi Ping BaZi practice instead uses the Lichun instant — see Year Pillar (Lichun boundary). Because the lunar new year wanders between about January 21 and February 20 while Lichun stays near February 4, the two boundaries usually do not coincide.
School differences
This is a genuine dispute inside the tradition, not an engine quirk: the same birth moment yields a different year pillar (and via the month-stem derivation, different month pillars) depending on which boundary a lineage uses. It is registered as entry D-01 in the project's School Dispute Register — both conventions are computed and shipped, with the selection recorded in the output rather than silently resolved. The related question of what happens during the boundary day itself (the whole new day vs the exact solar-term instant) is entry D-07.
How this engine computes it
- The lunar calendar (month starts, intercalary months, and hence Zhengyue Chuyi) is computed under the national standard rules and validated against the Hong Kong Observatory public–lunar conversion tables across 1901–2100.
- The engine's differential tests against the reference calendar implementation found agreement on all term dates; the only divergences from mainstream tools sit inside the boundary-day windows, explained by the date-vs-instant convention (D-07).
- The "lunar new year" and the "BaZi year pillar" are kept as two independent output fields; where they disagree for a birth moment, both are shown with the day gap between the boundaries.
Related entries
Year Pillar (Lichun boundary) — the solar counterpart, and the other half of this dispute · Early / Late Zi Hour · True Solar Time
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