"Now that I think of it, I've never had a raise in all these years," he joked recently.
Afterward, a few fans line up for autographs and pictures. But this is Hollywood, so most members act blasé, like it's an everyday thing. And it is. Harper, 46, says he'll keep teaching the class as long as there are people who will wait on line up to 90 minutes each Saturday to nab a spot in his class.
He says the same about "The Biggest Loser," which returns Tuesday night for Season 13 and a take-no-prisoners theme: "No excuses." There's also a (cruel) twist: Competitors show up at the ranch with a relative or friend believing they will compete as pairs and almost immediately learn they will actually be competitors.
"The producers are always looking for a twist, and this twist is pretty challenging," he said. "They come in in pairs, wanting to do it together, but then that gets taken away, so it's, "Uh-oh, I gotta do it for myself.' They have to find their own reason for being there."
It's a lesson Harper had to learn all over again this past year, which saw Michaels' departure and the introduction of trainers Dolvett Quince and tennis star Anna Kournikova, eager to prove themselves against Harper.
"This past year, it was 'Can I stand on my own without Jillian?' That's what it was like every day," he admits. "It's been an adjustment. But of course, life moves on. It's taken time to try to find our own footing."
Kournikova lasted only one season, for reasons that remain unclear. Harper dismissed rumors that she was difficult to work with. But he questioned whether she wanted the job after she got to try it on for size. "The job is all consuming," he said. "It's a lot to deal with, and it's not pretty.... Maybe she didn't have that kind of drive."
Although Harper says the "Biggest Loser" brand is really about the triumph of the competitors, not the trainers, he admits that a little of the magic is gone since Michaels' departure.
"It's hard to say precisely why it works, but we are the dynamic duo. We've got magic together," he said. "We fight like brother and sister and love each other like husband and wife."
Asked whether he could see Michaels rejoining the show, Harper said "I never say 'never.'"
"The Biggest Loser" continues to be a workhorse for the network, but its ratings have struggled. The Season 12 finale pulled in 6.79 million viewers. But that was down from the previous two finales — for Seasons 10 and 11 — which each pulled in at least 8.1 million viewers.
Harper seems surprised but then quickly points out that he tries to avoid the ratings drama.
He says he tries to live the same lessons he imparts to the morbidly obese men and women who show up each season, desperate for Harper's help: "Believe in yourself, trust the process, change forever."
"I'm doing what I was put on this earth to do — all the rest of that stuff, I don't care," he said. "At the end of the day, I'm a trainer. That's what I was doing before the show, that's what I do during the show, and that's what I will do after the show."