Why is there a leap month in the lunar calendar?

The reasons for leap month are as follows:

Generally speaking, the lunar year is 12 months. According to the orbit of the moon around the earth, the number of days in a month is 29 or 30 days. The leap year is 13 months. In China, the average lunar year is 353 or 354 days, and leap years are 384 or 385 days. Gregorian calendar year (also called tropic year), the annual average is about 365.2422 days (that is, the earth goes around the sun once). As a kind of lunar calendar, the number of days per month depends on the monthly profit and loss, and the time of one year is based on 12 months; In order to close the cycle of the earth around the sun, that is, the tropic year, one month is added at regular intervals, and the added month is a leap month, so the leap year of the lunar calendar is 13 months. There is no thirteenth month in the lunar calendar. According to the calendar rules, a leap month repeats the same month after any month, and the repeated month is a leap month. For example, the leap month after April is called leap April.