Kristen Bell's fiance Dax Shepard is reportedly "embarrassed" about his love's coupon obsession.

The 32-year-old actress is said to be keen on finding a good bargain and spends an inordinate amount of time scouring for deals.

Kristen has even dug through her neighbours mailboxes, a source tells America's Star magazine.

"[Kristen] spends hours a day looking for coupons," the insider said.

"Dax is just baffled and embarrassed by Kristen's cheapness. She's a multimillionaire but acts like she's nearly homeless."

The couple was engaged in 2010 and insiders are worried her extreme couponing may jeopardise their plans to wed.

"There's absolutely no way they will see their wedding day if she doesn't tone it down," the source said.

Kristen previously coyly revealed the extremes to which she will go to secure a discount.

"I'm not saying I did do it, but I may or not have stolen them out of my neighbours' mailboxes sometimes," Kristen laughed to American talk show host Conan O'Brien.

"I wouldn't have done it in the dark of night, but if I'm walking my dogs past and I see it sticking out, I may or may not have grabbed it more than once."