Amazon.com Inc. AMZN, +1.28% is expected to account for more than half of all e-commerce growth in 2015, Macquarie Research said in a Tuesday note. The bank raised its price target for Amazon's shares to $760 from $740. Macquarie estimates that for every $1 of e-commerce growth, Amazon will take 51 cents, and for every $1 of adjusted retail growth, Amazon will take 24 cents. "Think about the inverse of that: Every other retailer is fighting for 49 cents and 76 cents of each dollar, respectively," the bank wrote. Macquarie attributes Amazon's gains to Prime membership, which it said now reaches about 25% of U.S. households. The bank believes 50% of households will be Prime members by 2020. "While 2015 saw Amazon's stock appreciate 114% in large part based on Amazon Web Services, we believe that Prime will lead to more gains in 2016," the note said. Data from Slice Intelligence shows that 39.3% of e-commerce sales between Nov. 1 and Dec. 6 went to Amazon. The e-commerce company's shares are up 23.5% for the past three months while the S&P; is up 4.2% for the same period.