This site adopts one documented school convention, not a universal rule. Da Yun direction follows the polarity of the birth-year stem and sex recorded at birth. Forward charts measure to the next Jie; reverse charts measure to the previous Jie. Elapsed time converts at three days to one year. Other schools may use different solar markers, day boundaries, direction rules, or rounding.
How do you calculate the starting age for Da Yun in BaZi?
This implementation uses the common rule: Yang-year male and Yin-year female run forward; Yin-year male and Yang-year female run backward.
The year stem determines Yin or Yang. The sequence then moves forward or backward from the Month Pillar through the sexagenary cycle. If the user selects Other / unsure or Prefer not to say for sex recorded at birth, the site does not silently guess. It returns the natal chart without a definitive Da Yun direction, starting age, or luck-pillar sequence.
Step 1: decide whether the chart counts forward or backward
Use the birth-year stem polarity and sex recorded at birth under the disclosed convention. If that input is not supplied, show the natal chart and explain that Da Yun direction cannot be finalized.
Step 2: count from birth to the next or previous solar term
Forward charts measure to the next Jie boundary. Reverse charts measure back to the previous Jie boundary. The measured interval is an exact time distance, not a rounded calendar guess.
Step 3: convert elapsed days into years and months
The adopted ratio is three elapsed days to one year. Smaller units are preserved so users can audit why two displays may differ after rounding.
Which solar term is used?
Direction determines whether the calculation measures to the next Jie or back to the previous Jie.
The twelve Jie boundaries are used, not ordinary lunar-month boundaries and not the mid-term Qi markers. The solar-term instant must first be converted into the relevant timezone so the elapsed interval is measured between actual instants.
How is elapsed time converted to starting age?
The traditional conversion used here is three elapsed days to one year, one day to four months, and one two-hour period to ten days.
The engine retains the exact elapsed seconds, converts them proportionally, and derives a start date. The interface may display years and months for readability, but it does not discard the more precise source value. Rounding rules are versioned because different calculators may display the same underlying interval differently.
What happens near a boundary?
A boundary result is shown as uncertain rather than forced into one silent answer.
If the recorded birth time is approximate, the normalized standard time and true solar time cross a two-hour branch, day boundary, or solar-term boundary, the report should display the competing result and request confirmation. Historical timezone and daylight-saving data also affect the instant used.
Why can another practitioner show a different starting age?
Schools and software can differ on direction rules, which solar markers to use, Zi-hour boundaries, true solar time, elapsed-time rounding, and whether age is displayed nominally or exactly.
A difference is not resolved by asking an AI to choose a preferred answer. Compare the conventions and timestamps. This site stores the convention name, rule version, direction, source interval, start age, and start date so the result can be audited.
Can the calculation be reproduced?
These two examples expose the inputs, relevant Jie timestamps, direction, and stored result.
The astronomical solar-term engine is astronomy-engine 2.1.19. The adopted calculation convention is year-stem-sex-sect-2 with exact elapsed timestamps retained. Alternative schools may use different markers, rounding, sex or polarity conventions, or age display rules; those results should be labelled as a different convention, not silently mixed.
- Wuhan example: 11 Nov 1994 12:00 Asia/Shanghai, female, Yang year stem. Direction is backward. Previous Jie is Li Dong at 1994-11-07 23:35:57.746 +08:00. Stored start age is 1 year, 2 months, 2 days; start date 1996-01-13 12:00 +08:00.
- Tokyo example: 20 Mar 1988 18:15 Asia/Tokyo, male, Yang year stem. Direction is forward. Next Jie is Qing Ming at 1988-04-04 22:39:43.685 +09:00. Stored start age is 5 years, 0 months, 22 days, 2 hours; start date 1993-04-11 20:15 +09:00.
Where results commonly diverge.
Is Da Yun calculated from the Month Pillar?
Yes. The ten-year pillar sequence advances or reverses from the natal Month Pillar under the adopted direction rule. The starting age is a separate calculation based on the interval between birth and the relevant Jie boundary.
Does BaZi use Lunar New Year to calculate Da Yun?
Not in this implementation. The natal year and month pillars use solar-term conventions, and the Da Yun starting interval uses Jie boundaries. Lunar New Year is a civil and cultural date, but it is not the year-pillar boundary used by this BaZi calculation method.
Why does birth sex affect Da Yun direction?
The common traditional convention combines the Yin or Yang polarity of the birth-year stem with sex recorded at birth to select forward or reverse motion. This is a calculation rule, not a judgment of gender identity. Users may decline; the chart can still be calculated without a definitive Da Yun sequence.
Method and boundaries
BaZi is a traditional interpretive system with multiple conventions. The site separates deterministic calendar calculations from interpretation, versions its adopted rules, flags boundary cases, and does not present symbolic readings as scientific diagnosis or guaranteed prediction.
Use the deterministic calculator → Generate a chart and inspect the displayed rule and precision notes.