More than 40 percent of American shoppers have used a buy-now-pay-later plan, according to a recent Credit Karma/Qualtrics survey, with the highest usage among Gen Z and younger millennials. Of those who participated in a BNPL program last year, 27 percent were aged 19 to 25, while 48 percent were 26 to 34, according to Cardify.ai, a firm that tracks consumer spending data.