How does Zi Wei Dou Shu handle a leap month?
Meridian uses the split rule, which is the most widely taught. Born in the first fifteen days of a leap month and you count as that month. Born on the sixteenth or later and you count as the month after. It sounds administrative until you see what it moves.
Why leap months exist
The Chinese calendar tracks both the moon and the sun. Twelve lunar months fall about eleven days short of a solar year, so roughly every three years an extra month is inserted to stop the calendar drifting away from the seasons. That inserted month repeats the number of the one before it.
Zi Wei Dou Shu places the life palace by counting from the birth month. A repeated month number makes that count ambiguous, so a rule is needed.
What the split actually moves
2017 had a leap sixth month. Two births inside it, fourteen days apart:
| Born 2017, 07:30, Hong Kong | 1 August | 15 August |
|---|---|---|
| Lunar date | Leap month 6, day 10 | Leap month 6, day 24 |
| Counts as month | 6 | 7 |
| Life palace | 卯 | 辰 |
The life palace is the anchor of the entire chart. Every other palace is positioned relative to it, so moving it moves everything. Two people born a fortnight apart, both in the same leap month, read very differently.
Meridian applies the split rule and shows the working: the lunar date, whether it fell in a leap month, and which month the chart counted it as. If you were born in a leap month you will see that on your chart rather than having to know to ask. It is the kind of detail that separates a chart you can trust from one you simply receive.
If you were born in a leap month
Some schools do not split at all and treat the whole leap month as the following month. Others weigh the solar term rather than the day number. If your birthday falls near the middle of a leap month, read both charts and note which convention produced which.
This is not a defect in the tradition. It is what happens when a system built on two calendars meets a month that exists to reconcile them.
Sources
Related
- Why do two BaZi calculators give you different charts?
- Should a BaZi chart use clock time or true solar time?
- Born overseas: which time does your chart use?
See your lunar date and how it was counted
Worked example computed by Meridian's chart engines on 1 August 2026. The engines are deterministic, so the same input returns the same chart.
This page explains calculation conventions. It does not interpret a chart and is not advice.