Dive Brief:

Amazon Prime members convert 74% of the time on Amazon.com, says a new study from Millward Brown Digital, compared to 13% for non-prime members.

Prime members also showed a preference for Amazon, converting 6% of the time at other warehouse retailers’ e-commerce sites.

If membership growth for Amazon Prime continues at its current pace, half of all U.S. households could be Amazon Prime members by 2020.

Dive Insight:

Amazon Prime members not only convert more often, according to a new survey from Millward Brown Digital, they are loyal to Amazon, too. Members of the subscription loyalty program convert a whopping 74% of the time, or some 22 times more often than the average 3.32% for the nation’s top online retailers.

Non-members also convert at a greater rate when shopping Amazon, with 13% of visits leading to a sale. Prime has proven extremely effective at making Amazon shoppers’ go-to site, Millward Brown says, making the likelihood that a shopper will look for items at another general-merchandise site such as Wal-Mart or Target drop to less than 1%.

With these numbers, rival retailers will have to rethink their own loyalty programs or try to entice customers away from Amazon with other deals. One possible solution might be found in the new marketplace retailer Jet.com, which lets customers lower their shopping cart by adjusting different variables like basket size and shipping.

Investment firm Macquarie estimates that 40 million U.S. households are Prime members, and current growth rates could bring Prime to half of all households by 2020.