Apple has never disclosed unit sales for the Apple Watch and it’s entirely possible it never will. Especially now that Apple recently decided to keep iPhone unit sales a closely guarded secret, it stands to reason that we’ll never get official sales numbers for Apple’s smartwatch. Nonetheless, Apple executives have revealed that the Apple Watch continues to grow in popularity with each passing year. Driving the point home, Tim Cook during an interview last month said that revenue from the company’s wearable product line (which includes the Apple Watch and items like AirPods) is already higher than the revenue Apple saw from the iPod when the iconic music player was at its peak.

In light of that, new research from The NPD Group reveals that the smartwatch market overall is growing at an impressive clip and that the Apple Watch remains the runaway market leader at this point. Specifically, year-over-year smartwatch unit sales in the U.S. jumped by 61% while revenue jumped by 51%. As for specific revenue figures, the report relays that smartwatch revenue from November of 2017 through November of 2018 checked in at $5 billion. One particularly interesting data point is that 88% of all smartwatch sales can be attributed to Apple, Samsung, and Fitbit.

“Over the last 18 months smartwatch sales gained strong momentum, proving the naysayers, who didn’t think the category could achieve mainstream acceptance, had potentially judged too soon,” NPD analyst Weston Henderek said in a press release. “The ability to be truly connected via built-in LTE without the need to have a smartphone nearby proved to be a tipping point for consumers, as they now recognize the value in being able to complete a wide range of tasks on the device including receiving notifications, messaging, accessing smart home controls, and more.”

Indeed, Apple executives have pointed to the inclusion of LTE connectivity on the Apple Watch Series 3 as a huge selling point. Notably, Apple Watch sales during the 2017 holiday quarter were record-breaking. More recently, Tim Cook said that revenue from Apple wearables line jumped by 50% “thanks to strong sales of both Apple Watch and AirPods.”