Amazon Prime subscribers will more than double to 275 million in a decade, estimates Citigroup, which raised its price target on the stock Monday after a deep-dive analysis into the subscription service of the internet retailing juggernaut.

Citi analysts concluded that Wall Street does not appreciate the full value of the platform, projecting that the company could see more than $500 billion in Prime-related gross sales per year within a decade.

"We remain positive on Amazon shares and view Amazon's large and growing global Prime member base as not only a source of recurring revenue but a key reason why brands and third-party sellers are increasingly relying on Amazon's marketplace," analyst Mark May wrote in a note published Sunday.

May added that while investors can expect gross merchandise sales of $633 billion by 2029, shareholders should also prepare for reliable returns in the near term, including a 15 percent rally in share price to $2,250 over the next year. May's previous target was $2,100.

In terms of membership, Prime is also set for robust growth, May said. Amazon's 101 million paid subscribers at the end of 2017 now rival Netflix numbers of 117 million.

"Prime has been a tremendous success," May continued. "Prime members are growing 35 percent to 40 percent per annum. There are many benefits of having highly satisfied membership-based customers, but a simple metric is that most studies suggest Prime members spend twice as much as non-Prime members."

Citi now expects Prime subscriptions to top 275 million by 2029 as roughly 80 percent of U.S. households adopt the service. Further, May added that international members may still be warming up to the service, with overseas members spending $35 to $40 per month compared to the $120 per month spent by American Prime members.

The company currently offers Prime in 16 countries, including Japan, Germany, Canada and India.

Amazon's stock fell 0.67 percent Monday following the Citi note. Shares are up 65.8 percent so far this year and up over 100 percent over the last 12 months.