The Hindi filmmaker has received messages of congratulations from a number of other Bollywood directors.
Ram Gopal Varma, who is reported to share a fractious relationship with Johar, commented on Twitter: "Hey Karan wishing that even ur Ghums will turn into ur Khushis... Have a hundred Happy Birthdays! (sic)"
Johar was also sent video messages from Dostana director Tarun Mansukhani and Wake Up Sid filmmaker Ayan Mukerji.
"I still remember when I first got to know you. On your birthday you took all of us out to lunch, and that was fantastic and I had never had that before from a boss," said Mansukhani.
Johar is said to be spending the evening with Shah Rukh Khan watching the Kolkata Knight Riders IPL cricket match.