Why retired NFL star Rob Gronkowski never spent a dime of his NFL salary

Former New England Patriots star Rob Gronkowski announced his retirement in March, putting an end to a nine-year NFL career that saw him rack up three Super Bowl wins and five Pro Bowl appearances while he earned over $50 million.

The 30-year-old Gronkowksi, who goes by the nickname "Gronk," has since moved on to the next stage of his career. The former NFL star announced on Tuesday that he's partnering with CBD products company CBDMedic to create a line of topical pain treatments using the cannabis-derived compound.

While Gronkowski is still likely to embark on additional ventures in his post-NFL career — he told reporters on Tuesday that he could partner with his brothers on fitness-related projects and that he's open to the idea of competing on ABC's "Dancing With the Stars" — one thing that's certain is the former NFL star's frugal money habits during his playing days have set him up for a more comfortable retirement.

"I just wanted to [save money] throughout my NFL career because I know that — and I've seen it with my own eyes — that it might not last long," Gronkowski tells CNBC Make It.

During his nine-year NFL career, Gronkowski made a point of only spending the money he made from various endorsement deals he signed with brands like Dunkin' Donuts, Tide laundry detergent and Monster Energy that reportedly earned him more than $3.5 million over his career. That way, he could save the millions he earned playing for the Patriots.

In fact, Gronk never touched "one dime of my signing bonus or NFL contract money," he wrote in his 2015 book, "It's Good to be Gronk."

While Gronkowski earned a total of $53.4 million from his NFL contracts, according to Spotrac — he retired before the final season of the six-year, $54 million deal he signed with New England in 2012 — he says watching some other athletes blow through their own multimillion-dollar contracts inspired him to always keep a sizable nest egg.

In a sport where the average NFL player's career length is only 3.3 years, Gronkowski says he always tried to remember that his lucrative playing days could end in a flash, so he wanted to be sure he had enough money saved to steer him through post-football life.

"The way I played it, I feel like I'm in a totally safe spot, which is great," Gronkowski tells CNBC Make It. "I've seen other players, you know, not be in a safe spot after they're done playing, and [they] go and spend it all. It's just great to have that feeling and to have that security that I can go out there trying new adventures [and] put all of my marbles on it, but know I'm still safe in the back end."

Of course, just because Gronkowski saved the bulk of the millions he's earned since he entered the NFL in 2012, that doesn't mean he's completely immune to splurging when the mood strikes. (He did spend $1.9 million on a Boston penthouse in 2016 before selling the condo in April for $2.3 million.)

"I ain't gonna just save it all, I like to splurge a little bit," Gronkowski says with a chuckle.

In fact, in 2018, Gronkowski revealed on an episode of Uninterrupted's "Kneading Dough" that he'd finally broken down and splurged on an expensive piece of jewelry. After becoming enamored with a friend's necklace, Gronkowski said at the time, he bought his own diamond chain. "I never had jewelry in my life. [My friend] let me wear it last year at a party and it made me feel good," he said on the podcast.

That necklace, which he says cost six figures, is still Gronkowski's biggest splurge on an unnecessary item, he tells CNBC Make It: "Yes, for sure."

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Rob Gronkowski #87 of the New England Patriots

Scott Halleran | Getty Images

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