New York: As Google celebrated its 18th birthday with an animated, festive-balloon Doodle on Tuesday, there were some confusion regarding the date as the search engine giant has celebrated its birthday on other days in the month of September in the past. The company was founded by Larry Page and Sergey Brin in 1998. The company's own history lists its incorporation date in 1998 as September 4. Since 2006, Google has celebrated its birthday on September 27, but the year before that, had it as September 26. "In 2004, its 6th birthday Doodle went online on September 7 and in the year before that, it was September 8," the Telegraph reported. Google has celebrated its birthday with a Doodle every year since its fourth birthday in 2002. In fact, Google has spent much of the month of September, celebrating its birthday with sending out posts and decorating Googleplex - the corporate headquarters complex of Google and its parent company Alphabet Inc at Mountain View, Santa Clara county, California.