He'll sometimes wear a favorite pair of jeans "seven days straight," he said, adding: "I make sure I throw them in the washer, like, day three."

He's particularly frugal when it comes to his wardrobe. "My 'broke habit' still is my clothing and shoes," he told Maverick Carter on a new episode of UNINTERRUPTED 's "Kneading Dough." "If I like the clothing, if I like the shoes, I'll wear those shoes and I'll wear that clothing down to the rags."

In fact, Gronkowski still hasn't touched a dime of his career NFL salary or signing bonuses and has chosen instead to live off of his endorsement money .

New England Patriots star Rob Gronkowski is slated to earn $8 million in base salary in 2018 . After factoring in bonuses and endorsements, he'll bring home even more. But just because the NFL star earns a lot doesn't mean he spends a lot.

Wearing the same thing and getting the most out of his clothes is a natural habit, said Gronkowski, who grew up using hand-me-downs from his brothers: "Whatever my brothers had — hockey equipment, baseball equipment, even clothes — [my parents] used to just hand it down to us kids. That's why I just feel like I have no problem ever just wearing the same shirt, wearing the same jeans, shorts, until I totally got to finally get rid of them."

He's not the only high-earner who keeps his wardrobe simple: Self-made millionaire and former "Tonight Show" host Jay Leno refuses to spend a lot of money on what he wears. "I'm not a big shopping guy. I'm just not interested in clothes" outside of the essentials, he tells CNBC Make. "To me, it seems like a complete waste of money. I just want to have enough clothes to cover legally what parts I have to cover."

Gronkowski, who only just splurged on his first luxury item after being in the NFL for eight years, told Carter that his spending habits may change when he retires from football: "I'll probably spend a little bit more. … When you're playing six months of the year, you're just driving home and driving to the stadium and you're not really doing anything out and about. So when you have a full year of free time, I would say that I would be spending more money."

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