What changes when you round a BaZi time-zone offset?

Why “that day” cannot settle a pillar

A solar term is not a whole day; it is an astronomical instant. The 24 solar terms divide the sun’s position along the ecliptic, and each term begins at a specific moment. The year pillar changes at the Li Chun transition, and the month pillar changes at the relevant jie term. Two births on the same date can therefore land on different year or month pillars depending on which side of the transition they fall. Treating “the day of Li Chun” as one block merges two different instants.

This is also why a pillar cannot be inferred from the date. A date gives an interval; the transition instant gives the dividing line. Wenbu’s published notes state that the year and month pillars compare the birth’s absolute instant with the solar-term instant, using fixed UTC+08:00 without adding historical daylight saving. In other words, first restore the birth record to an absolute instant, then compare it with the solar-term instant — do not read the pillar off the calendar day.

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The boundary worksheet: four inputs, one mark per pillar

Write the Gregorian birth date on the first line, the local clock time with its precision on the second (for example “about mid-morning” or “08:37 recorded”), the birthplace IANA zone name on the third, and the relevant solar-term instant on the fourth. If any of the four is missing, the judgment stops at “open.” If the original record has only a date and no time, the year and month pillars near a transition cannot be settled; in that case Wenbu provisionally uses local noon for the year and month pillars and flags uncertainty on solar-term days, and that provisional value should not be treated as confirmed.

Then mark each pillar. The year pillar is “settled” only when the order of the birth instant and the Li Chun transition is clear. The month pillar is “settled” only when the order of the birth instant and that month’s jie transition is clear. The day and hour pillars are a separate layer: they default to the selected local clock and are affected by the day-boundary rule and the apparent-solar-time setting. This worksheet does not handle the 23:00 Zi day boundary, and it does not handle offset or daylight-saving conversion details; those belong to the other two guides.

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Record precision sets the strength of the conclusion

“08:37” and “a bit after eight” are not the same kind of evidence. If the solar-term instant falls outside the interval covered by the record’s precision, the conclusion is stable; if it falls inside, the honest answer is “open.” Suppose the record says “about mid-morning” and the transition is at 10:42: an earlier and a later birth in that morning would give different results, so no single pillar should be chosen. Keeping both possibilities and noting “birth record too imprecise” is more useful than a pillar that looks certain.

Separate calculation uncertainty from interpretive uncertainty. Even when a pillar is settled, whether a traditional interpretation holds is a different question; a calculation can be reproduced by convention without the interpretation being scientifically validated. The worksheet addresses only the first: it lays out the inputs, the instants and the dividing line so another person can check them. It does not judge which interpretation is better, and it does not choose a school for the reader.

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Common mistakes and the limits of this page

The first mistake is treating Lunar New Year as the year-pillar boundary. The year pillar changes at the Li Chun transition, not at the first day of the first lunar month, so births around Spring Festival are especially easy to misjudge. The second is applying apparent-solar-time correction to the year and month pillars. Wenbu’s notes say that with the correction enabled, the day and hour pillars use an approximate longitude and equation-of-time adjustment, while the year and month pillars still use the original absolute instant; applying the correction again to the transition comparison introduces a new error.

The third mistake is guessing a time zone from historical jurisdiction. This page does not supply, and will not invent, historical administrative rules; what is needed is the birthplace’s IANA zone name and the offset actually in effect on that date. If a local clock time was skipped or repeated during a daylight-saving change, Wenbu’s chart rejects such ambiguous or nonexistent input, so supply an explicit UTC offset instead of picking one arbitrarily. The solar-term instant itself is an astronomical calculation, separate from local clock adjustments.

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Questions you may have

Terms in this guide

Solar-term transition instant

The specific astronomical moment at which a solar term begins; it is the boundary for changing the year and month pillars, not a whole day.

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Absolute instant

The point in time fixed by the birth date, local clock time and birthplace zone, used for comparison with the solar-term instant.

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Open

A mark for a pillar when the birth record’s precision cannot establish whether the birth came before or after the solar-term boundary; both results must be kept.

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Fixed UTC+08:00 standard time

The UTC+08:00 standard used by Wenbu when comparing the year and month pillars with solar-term instants, without adding historical daylight saving.

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