Katharine McPhee's Baby Bump

American Idol alum Katharine McPhee is workin’ at the car wash on Tuesday on the Los Angeles set of I Know What Boys Like, in which she plays a pregnant hippie student.

“Today is the first day I’m wearing the prosthetic belly, which wraps all the way around [to] my back, and it’s actually really comfortable,” Kat revealed to Entertainment Tonight. “I’m really enjoying it. It’s hot and sweaty though, but it’s like Method acting.”

“I think it’ll probably hold me off a bit on having a baby,” she adds. “I [do] definitely want to have a baby, and it’s fun to just pretend and look in the mirror.”