40% of online shoppers always or sometimes save their payment information on a retailer’s website or in an app, according to a new CreditCards.com report.

Princeton Survey Research Associates International conducted the study via telephone interviews of 1,002 U.S. consumers in May.

The survey found that about 62% of 234.6 million U.S. adults shop online and of them, 65% of consumers, or 94 million, have their payment information saved on a website. 10% say they always saved their credit or debit card information on the website or in app to make future purchase, 30% say they sometimes do, 25% say rarely and 34% said never. The remaining consumers didn’t know or refused to answer the question.

Online retailers should add a feature that allows shoppers to save their credit card credentials, because it makes buying again more convenient, says Matt Schulz senior industry analyst for CreditCards.com.

“It is a way to judge loyalty,” Schulz says. “If someone chooses to store their card information on your site, they’re clearly making a commitment to you. They would almost certainly be more likely to buy from your site again than someone who didn’t store their info.”

If a retailer allows consumers to save their credit cards to the website or app, it speeds checkout and makes it easier for future purchases, Schulz says. For this reason, in addition to saving credit and debit card information, many online retailers in the Internet Retailer 2017 Top 1000 offer expedited checkout buttons on their site, for example, 459 Top 1000 retailers have a PayPal button and 68 retailers offer Visa Checkout, according to Top500Guide.com.

Quick checkout is especially important on mobile devices, where shoppers have shorter attention spans and are less patient when it comes to waiting for websites to load. In fact, 10.7% of consumers cite a website or app as too slow as a frustration when shopping via a smartphone and 4% said checkout takes too long, according to an exclusive Internet Retailer survey of more than 2,500 U.S. consumers conducted in March 2017 by Bizrate Insights.

That same study found that 54.7% of consumers say they are shopping more on their smartphones now than they were a year ago, and 10.2% of them say the reason is because they have stored payment data on their phone so it is easier to check out.