The Chinese lunar calendar is a traditional calendar in China and it is also called Xia Li, Zhong Li, Jiu Li, or Yin Li. It is based on exact astronomical observations of positions of the sun and moon. Thus in essence it is a combined solar/lunar calendar.

In the calendar, one year is divided into 12 months and the months have either 29 or 30 days, always beginning on days of astronomical new moons. So each year has 354 or 355 days. To make the average length of the years equal to a tropical year, an intercalary month is added every two or three years.

As a result, an ordinary year has 12 months while a leap year has 13 months. And an ordinary year has 354, or 355 days, and a leap year has 384 or 385 days.