Harry Potter fans pose for the photographers during 'Harry Potter and The Deathly Hallows Part 2' premiere at the Callao cinema on July 7, 2011 in Madrid, Spain.
Harry Potter fans pose for the photographers during 'Harry Potter and The Deathly Hallows Part 2' premiere at the Callao cinema on July 7, 2011 in Madrid, Spain. - 
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Jeremy Hobson: The final Harry Potter movie opens in theaters today. So far the films have grossed $6.4 billion worldwide and the Potter brand as whole is estimated to be worth $15 billion. But with no new books or movies planned, how long can the boy wizard keep conjuring up profits?

Sanden Totten reports.

Sanden Totten: Believe it or not, Harry Potter is over the hill. Or at least the brand is, according to marketing professional Susan Gunelius. She wrote the book, Harry Potter: The Story of a Global Business Phenomenon. She says every brand hits a peak and then declines in value.

Susan Gunelius: So the challenge for the Harry Potter brand right now would be finding ways to slow that decline cycle.

Gunelius says J.K. Rowling and the Potter marketing team are off to a good start. Last month, they unveiled a website called Pottermore, a place where fans can test out digital spells, get sorted into Hogwarts houses and buy e-book versions of the Potter saga.

Gunelius: This is a brand that can't decline significantly any time in the near future. There is too much invested in it from the corporate perspective.

Gunelius guesses that with even with no new content, Harry Potter has at least 10 years of solid profits left. After all, Warner Brothers has DVDs and movie merchandise to sell. Universal Studios spent over $200 million on its Wizarding World of Harry Potter theme park.

And of course, there's the mom-and-pop wand shops.

Stan Goldin: We sell probably around 50 to 100 wands per week.

That's Stan Goldin, owner of a Potter-themed gift shop in L.A. called Whimsic Alley. Goldin says he opened the store when Potter fever was sweeping the nation, but he thought about closing it last year.

Goldin: The last book had already come out. There were a couple more movies set to come out but I didn't know what would happen after that, whether there would be any longevity in this franchise.

But instead of closing, Goldin expanded into a bigger building, and he says sales keep climbing every month. But even Goldin wonders how long it'll be before a chapter titled "Harry Potter and The Point of Diminishing Returns."

Of course, if you ask 16-year-old Madison Mojica -- who was checking out the wands at Whimsic Alley -- Potter vendors have nothing to worry about.

Madison Mojica: We're the Harry Potter generation; it's never going to die for us.

If fans like her turn out to be right -- the spell could last for decades.

I'm Sanden Totten for Marketplace.

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