How to Chart a Leap Lunar Month

The Chinese lunar calendar tracks new moons, resulting in about 354 days per regular 12-month lunar year—roughly 11 days shorter than the 365.24-day solar year. To keep seasons aligned, a leap (intercalary) month is inserted 7 times every 19 years. For example, 'Leap April' follows regular April, repeating calendar dates without adding a 13th stem-branch pillar to Ba Zi.

In Four Pillars astrology, Month Pillars are strictly demarcated by the 12 major solar nodes (Jie) of the 24 Solar Terms: Yin starts at Li Chun, Mao at Jing Zhe, Chen at Qing Ming, Si at Li Xia, Wu at Mang Zhong, and so forth. Month transitions are completely independent of lunar first-of-month days.

The most common mistake is assuming 'Leap April' is automatically the Si month or treating it as the following month. The Month Pillar sets the seasonal command (Yue Ling) of the entire chart; miscalculating it invalidates Day Master strength and all Ten Gods configurations.

Step 1: Confirm the lunar year, month, date, and leap status. In leap years, regular month X and leap month X are roughly 29 to 30 solar days apart; missing the leap flag shifts the underlying solar date by nearly an entire month.

Step 2: Convert the leap lunar date into a standardized Gregorian solar timestamp (year, month, day, and time) using an astronomical perpetual calendar.

Step 3: Check which solar term the Gregorian date falls under. For example, for a 'Leap April' birthday: if the solar date falls before 'Mang Zhong' (around June 5–6), the Month Pillar is still 【Si month】; if it falls after Mang Zhong, it enters 【Wu month】. The true Month Pillar depends entirely on the solar term position.

Step 4: The Hour Pillar continues to follow standard two-hour branch intervals. A leap month alters the solar day of birth, not the rules governing hours within that day.

Family records and elders often recall birthdays purely in traditional form, such as 'Leap May, 6th day', without knowing the Gregorian equivalent. Do not arbitrarily convert this into regular May or June.

In TianJiGe, select 'Lunar' calendar mode and choose the month marked with 'Leap' (e.g. 'Leap May'). The system automatically computes the astronomical solar conversion and applies the correct solar term boundaries.

If using basic calculators without leap month support, consult a verified perpetual calendar first to convert the date to its exact Gregorian equivalent, then chart using solar input.

First, verify the 【Year Pillar】: For births near the lunar new year or winter leap months, verify the Year Pillar against 'Li Chun' (Start of Spring), not Chinese New Year's Day (Spring Festival).

Second, verify the 【Month Pillar】: Ensure the month branch stems from the active solar term rather than the lunar month name. Lunar 'May' is not synonymous with 'Wu month', and 'Leap May' must not be arbitrarily assigned to Wei or Wu.

Once Year and Month pillars align with solar terms, Day and Hour pillars are interpreted under standard rules. A leap month is an astronomical calendar mechanism, not a predictor of unique fortune or destiny.