BaZi methodology
Why do BaZi calculators give different results?
The same person, the same birth moment — yet two BaZi calculators may disagree on the day pillar or even the month pillar. Usually nobody is wrong: the differences come from a handful of real conventions and calculation choices. This guide walks through each one, and how FateSpectrum handles it.
1. Time zones & birthplace
BaZi runs on clock time, and clock time depends on the zone. The most common tool-to-tool difference is timezone resolution: matching the birthplace to the IANA timezone database versus asking the user to pick. One hour off changes the hour pillar. FateSpectrum resolves your birth city to its IANA timezone automatically and also uses the birthplace longitude for its calculations.
2. True solar time
Tradition reads the local sun, not the local clock. True solar time = local clock time + the equation of time + (birthplace longitude − standard meridian) × 4 minutes. Near an hour boundary — a 14:55 birth, say — applying it or not yields different hour pillars, and some calculators skip it. FateSpectrum applies true solar time to hour pillars, and the day pillar flips at 23:00 solar (Zi start).
3. Historical daylight saving time
Whether DST counts — and which year's rules apply — changes the clock-to-solar conversion. DST rules have changed repeatedly over history (start dates, amounts, whether it existed at all); some tools back-solve historical moments with today's fixed offset, which misplaces the chart. FateSpectrum follows the rules in force at the birth time, including clock gaps and overlaps.
4. Solar terms (month-pillar boundaries)
Month pillars change at each of the twelve 节 terms. Terms are astronomical instants — they shift every year by hours, so a birth hours before or after a term can resolve to different month pillars under a fixed-date table versus an astronomical calculation. FateSpectrum computes solar terms astronomically.
5. Day-boundary conventions
The Zi hour straddles midnight, and schools differ on when the day pillar flips: at Zi start (23:00 true solar), at midnight, or by recording early/late Zi separately. Each school has a lineage behind it and none is universally accepted. FateSpectrum uses the Zi-start convention in true solar time.
6. Why your hour pillar may differ
The hour pillar is where calculators diverge most, because it is a triple conversion: timezone resolution → true solar time (equation of time + longitude) → the two-hour boundary. A different choice at any step changes the pillar for births between 23:00–01:00 or a few minutes before an hour mark. If two charts differ only in the hour pillar, check the source of the birth time and the timezone first.
7. Calculation methodology
Ephemeris precision (astronomical formulas versus lookup tables), how centuries-old moments are back-solved, even rounding — boundary cases can differ without anyone calculating wrongly. These are precision and convention differences, not errors.
Calculate your BaZi chart with FateSpectrum
Every convention above — true solar time, historical DST, astronomical solar terms and the Zi-start day boundary — is implemented in our calculator.
Note: this guide describes conventions and calculation differences; it does not judge which school is correct.