IDC also lowered its Apple Watch forecast to 15.9 million shipments in 2015, down from 22 million, a 28% reduction. That's partly because more details have surfaced and the sales date of April 24 was later than IDC had previously expected, according to IDC analyst Ryan Reith in an email.
Even with that reduction, the Apple Watch will account for 62% of the smartwatch market in 2015, Reith said. IDC had expected the 22 million in Apple Watch shipments for this year in a forecast conducted last August, well before the shipment date and other details were announced at Apple's Spring Forward event on March 9, Reith said.
A February forecast by CCS Insight put potential Apple Watch sales at 20 million in 2015. Apple Watch goes on sale April 24, starting at $349, but some gold-encased models will start at $10,000. Apple will begin taking pre-order April 10.
IDC grouped the Apple Watch with Motorola's Moto 360, several Samsung Gear watches and others under a category it calls smart wearables, or devices capable of running third-party apps. For all of 2015, IDC said 25.7 million smart wearables will ship, up 511% from the 4.2 million shipped in 2014.
"The Apple Watch raises the profile of wearables in general and there are many vendors and devices that are eager to share the spotlight," said IDC analyst Ramon Llamas, in a statement.
Reith said the Apple Watch "will sell well, but price will be a hurdle, as well as the fact that it is a first-generation device and a lot of people tend to wait and see on first generation."
IDC also said that wearables in general will reach 45.7 million in 2015, up 133% over last year. Those include what IDC calls "basic wearables" -- those that don't run third-party apps -- as well as wearable devices worn on clothing, eyewear and other devices.
Reith said fitness bands such as the FitBit have led an explosion in wearables, and noted that prices for these have come down significantly. "Meanwhile, the market is quickly shifting toward higher-priced devices that offer greater functionality," Reith added.
"While Apple's entry into the market is symbolic, the key to success will be to create compelling use cases for the average consumer," Reith said in a statement. "Many users will need a good reason to replace a traditional watch or access with a wrist-worn device or some other form of wearable that will likely require daily charging and occasional software upgrades."