Hello, I'm an expert in Chinese culture and traditions. In the Chinese lunar calendar, a leap year is determined by the presence of an extra month. This is done to keep the lunar calendar in alignment with the solar year. Unlike the Gregorian calendar, which has a fixed leap year pattern every four years, the Chinese lunar calendar has a more complex system for determining leap months.

In the Chinese lunar calendar, a leap month is added approximately every 3 years to account for the difference between the lunar year (about 354 days) and the solar year (about 365 days). The decision to add a leap month is based on the timing of the lunar month and the position of the sun in the solar year. The 24 solar terms, or "jie qi," are used to guide this process, and a leap month is added if the first day of a new lunar month does not occur at least 54 days after the last "major" solar term of the previous lunar month.

So, to answer your question, a Chinese leap year with an extra month occurs irregularly, but on average, it happens about once every 3 years. However, it's important to note that the exact timing can vary, and it's not a fixed pattern like in the Gregorian calendar.

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Chinese Calendar Has Leap Months. While our modern Gregorian calendar adds only 1 leap day on February 29 nearly every 4 years, the Chinese add a whole leap month every 3 years. The Chinese Calendar has a leap month added about every three years. The name of a leap month is the same as the previous lunar month.read more >>