One of the most popular Katy Perry shows of 2018 was Saturday February 3rd at Tacoma Dome. Interest for that show was at its highest when ticket sales began. The interest resulted in high ticket prices that dropped as the show neared.
Across all Katy Perry shows in 2018, interest was strongest right when the shows were announced and tickets went on sale. Meanwhile, ticket prices typically fell about 25 - 30% from the date a show was announced until the days leading up to the show.