Abstract: It is most likely to make clear the birth year of Confucius. He should have been born in the 21st year of LU Xianggong. The opinion that Confucius be born in the 22nd year of LU Xianggong has been mistakenly caused by transformation from his real age to nominal one. Moreover, the transfer from the Zhou calendar to the Xia one should be responsible for such mistake. It is unbelievable that Confucius was born in Xia calendar August 21 or 27. In a word, he should have been born in Xia calendar December 23 of the 21st year of LU Xianggong.