The market for wearables is expected to post an 18.4% compound annual growth rate from 2017 to 2021, according to new data from market intelligence company International Data Corporation.

Basic wristbands such as Fitbits have been leaders in this area for some time, but Framingham, Massachusetts-based IDC said the number of watch shipments will account for much of the sector's future growth, going from 61.5 million in 2017 to an expected 149.5 million in 2021 as fashion brands and other companies get into the game.

"What will merit continued observation is how the market evolves beyond its current status and how users will either replace or append to their current devices," said Ramon Llamas, who is a research manager for IDC's Wearables team. "Tomorrow's wearables will become more fully featured and multi-functional, spanning health and fitness to communication and productivity. Effectively, that will make today's wearables seem quaint, and spur upgrades and replacements.