Prime has been an important initiative for the company, with research showing that members spend nearly double what non-members do per year on the site.
To make membership more attractive, the company has poured money into original content and football streaming, with analysts estimating that it spent $4.5 billion on non-sports programming in 2017. CEO Jeff Bezos has even quipped that Amazon was the first company to use a Golden Globe to sell toilet paper after its show "Transparent" won the award in 2015.
Here's what Amazon's chief financial officer Brian Olsavsky said about Prime's new price on the earnings call:
"The value of Prime to customers has never been greater. And the cost is also high, as we pointed out especially with shipping options and digital benefits, we continue to see rises in costs. So effective May 11, we're going to increase the price of our U.S. annual plan from $99 to $119 for new members. The new price will apply to renewals starting on June 16. Prime provides a unique combination of benefits, and we continue to invest in making this Prime program even more valuable for our members. As a reminder, we haven't increased the U.S. annual price Prime since our single increase, which was in March of 2014."
While Olsavsky cites rising costs, he doesn't provide information on exactly how much Prime costs the company per user, though Bezos has famously said that Amazon is a company that always tries to figure out how to charge people less, not more.
In Amazon's first quarter earnings, its "subscription services revenue," which includes Prime memberships, grew 60 percent to $3.1 billion and its earnings-per-share more than doubled since last year.
Correction: The original version of this story misstated the effective start date of the price increase.