The temple’s annual Brahmotsavam event is the biggest draw and lakhs of people visit Tirupati during this time. The event is a nine-day long festival here that takes place sometime during the latter half of the year. As the dates change year after year, it is best for you to check with the Tirumala Tirupati Devasthanam website to acquaint yourself with the exact dates for the current year before you plan a trip. It is also common practice for many people to arrive in Tirupati on December 31st of every year, visit the temple on that date and on January 1st and return. This is why the week starting December 25th is usually very crowded too every year.