What is Leap June (闰六月)?

In 2025, the Chinese lunar calendar features an extra month—Leap June—occurring from July 25 to August 22 in the Gregorian calendar. This phenomenon is due to the lunisolar calendar system, which aligns the lunar phases (based on the moon) with the solar year (based on the sun).

Why does it happen?

A typical lunar year has 354 days, while a solar year has 365.24 days, creating an 11-day gap.

To prevent seasonal drift (e.g., summer festivals occurring in winter), ancient Chinese astronomers introduced leap months every few years.

The rule: If a lunar month lacks a "Zhongqi" (solar term, like "Great Heat" or "End of Heat"), it becomes a leap month of the previous month39.

2025’s Leap June:

Normal June (June 25–July 23) includes the solar term "Great Heat" (大暑, July 22).

The following month (July 24–August 22) only has "Start of Autumn" (立秋, August 7) but no "End of Heat" (处暑, August 23), so it’s deemed Leap June39.