Four pillars · Four boundaries
Four Pillars boundary conventions
Almost every disagreement between two Chinese astrology sites comes down to a boundary: when a year turns, when a month turns, when a day turns. Different schools use different boundaries. This page states the conventions used here.
When the year turns
Two boundaries are in common use and they disagree by days or weeks. Popular sources turn the animal year at Chinese New Year. Four Pillars practice turns the stem-branch year at 立春 Lìchūn, the solar term that opens spring, which falls in early February regardless of where the new moon lands.
The profile leads with the Chinese New Year reading. When a birth falls between Chinese New Year and Li Chun, the Li Chun reading appears beside it. A birth on 10 February 2021 is a Rat year under the Chinese New Year boundary and an Ox year under the Li Chun boundary.
When the month turns
The stem-branch months begin at the twelve 節 solar terms — 立春 opens the Tiger month, 惊蛰 the Rabbit month, and so on. These are astronomical events, not calendar dates: 立春 fell on 3 February in 2021 and 4 February in 2024.
Each solar term is recorded as an exact moment in China Standard Time, then converted with the birth-place UTC offset supplied to the calculator. On a local boundary day, the birth time decides which side of that moment the chart occupies: 立春 2021 occurred at 22:58 CST, so a birth in China that morning still belonged to the previous month.
When the day turns
The day pillar carries the 日主 Day Master, the stem that stands for the person. Schools disagree about the 23:00 hour: under 晚子時 it opens the following day, while others hold the day at civil midnight.
Charts here follow 晚子時. A birth in that hour shows both readings, because the whole chart moves together — the hour stem is derived from the day stem, so a shifted day carries a shifted hour with it.
The hour convention
The twelve two-hour periods run from the Rat hour at 23:00. A time is read as local civil time exactly as given.
No correction is applied for birthplace longitude, true solar time, or daylight saving in force at the time. Practitioners who apply those corrections may place a birth near the edge of a period in the neighbouring one. Without a birth time, the hour pillar remains blank.
Calendar data
Where the calendar data comes from
Chinese New Year dates cover 1901 to 2100. Solar-term records use China Standard Time (UTC+08:00); calculators convert those moments to the fixed birth-place offset entered with the chart.
- Supported birth dates
- 19 February 1901 through 8 February 2100
- Outside that range
- Enter a date within the supported range.
Calendar references are listed in the source register.