Carrie Underwood has extended her Play On tour with dates scheduled through Dec. 19. The current leg of her tour continues through a June 20 show in Saskatoon, Saskatchewan. With four festival appearances scheduled in July and August, she returns to the road for a Sept. 25 concert in Portland, Ore., and almost 50 additional stops before ending the tour in Calgary, Alberta. She will have performed more than 100 shows in 2010. Billy Currington and Sons of Sylvia will appear as special guests during the fall tour. Underwood is donating 36 cents of every ticket sold during the fall tour to Save the Children’s United States Programs. This initiative was inspired by a reference to “36 cents” in the lyrics of her “Change,” a track from her Play On album which addresses how even the smallest bit of spare change can make a difference in the world. She’ll perform the song on American Idol during the “Idol Gives Back” episode airing Wednesday (April 21).