IDC’s latest forecast predicts that the new larger iPhone will help shipments of phablets surpass shipments of portable PCs by the end of the year.

IDC expects phablets, defined by the research firm as smartphones from 5.5-inches to less than 7 inches, to hit 175 million units by the end of the year compared to the 170 million portable PCs it expects will ship in 2014. It also said today that it expects phablet shipments to top 318 million units in 2015, which means the category is also on track to surpass tablet shipments by next year.

Apple is of course about to contribute to phablet sales with one of its two yet to be unveiled iPhone models expected to sport a 5.5-inch display when introduced later this month. IDC has factored Apple’s entrance into the category into its growth predictions for phablets:

It’s worth noting that IDC’s portable PC category doesn’t include any kind of desktop PC, tablet, or hybrid device with a detachable keyboard like the Surface. As you can see in IDC’s graph above, it expects shipment volumes of portable PCs to remain flat through 2018, while phablets will go from approximately 175 million units this year to an impressive 592 million over the same time period. That will take phablets from 9.8% market share of all connected devices this year (including all PCs, tablets, hybrids and smartphones) to 24.4% by 2018 at the expense of market share for “regular smartphones” and all other categories.

“With Apple expected to join the space in the coming weeks, we anticipate even more attention on phablets as larger screen smartphones become the new norm,” said Melissa Chau, Senior Research Manager with IDC’s Worldwide Quarterly Mobile Phone Tracker. IDC expects phablets to grow from 14.0% of the worldwide smartphone market in 2014 to 32.2% in 2018.

Apple is expected to unveil its new two iPhone models in 4.7-inch and 5.5-inch variants at its press event later this month on September 9.