The firm said it still expects the figure to stand at 57.7 percent above 2012 shipments, in spite of its updated data.
The reason behind the adjustment to 2013's figures is a quiet patch in the news cycle, which has been lacking significant tablet announcements.
It was, in part, to be expected. IDC said earlier this month that tablet shipments showed a sign of slowing in the second quarter, ahead of an expected next-generation iPad on deck for later this year.
"A lower than anticipated second quarter, hampered by a lack of major product announcements, means the second half of the year now becomes even more critical for a tablet market that has traditionally seen its highest shipment volume occur during the holiday season," said IDC research director Tom Mainelli.
IDC noted year-over-year it has started to see a maturity in the commercial segment of the market. From 10 percent in 2012, to 13 percent in 2013, the worldwide tablet market share is expected to reach 20 percent at least by 2017 in vertical markets, such as retail.
"Much of the long-term growth will be driven by countries like China where projected growth rates will be consistently higher than the worldwide average," IDC's Jitesh Ubrani said in prepared remarks.