Fourteen percent of US households with credit cards had signed up for the payment option by the end of September, up from 11 percent in February, Phoenix Marketing International said at a payments conference in Las Vegas.
"A very rapid initial threshold was achieved by Apple Pay and it is still growing but the growth rate has slowed down," said Greg Weed, director of card performance research at Phoenix.
An Apple spokeswoman declined to comment, but noted that a company statement in early October cited "double digit monthly growth in Apple Pay transactions" since its launch.
About 48 percent of Gen Xers, in their mid-30s to mid-50s, use Apple Pay, compared with 42 percent of millennials, aged 21 to 34, Phoenix said.
Among Apple Pay users, 86 percent have linked their credit cards to make a purchase, 49 percent consumers use their debit cards and 22 percent use different types of prepaid cards, the report showed.
Phoenix said it has been researching Apple Pay since its launch in October 2014, with a group of 15,000 consumers.
In June, two-thirds of the top 100 US retailers told Reuters they did not plan to accept Apple Pay this year.
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