Amazon is raising its monthly Prime membership rates 18 percent.

The premium membership that grants faster shipping and access to Amazon Video will now cost $12.99 per month, up from $10.99, according to the company's membership page.

Amazon is also increasing the discounted student monthly rate from $5.49 to $6.49 per month for new sign-ups.

The cost of a yearly membership, $99, will not change.

Recode first noticed the new price.

Amazon started the monthly pricing model less than two years ago as a more flexible way of taking advantage of Prime's fast shipping and other benefits. Prime members spend considerably more on Amazon than non-Prime members.

Amazon issued this statement Friday morning:

"Prime provides an unparalleled combination of shipping, shopping and entertainment benefits, and we continue to invest in making Prime even more valuable for our members. The number of items eligible for unlimited Free Two-Day Shipping increased in recent years from 20 million to more than 100 million items. We have expanded Prime Free Same-Day and Prime Free One-Day delivery to more than 8,000 cities and towns. We also continue to introduce new, popular and award-winning Prime Originals, like The Grand Tour, Sneaky Pete, and the Golden Globe-winning The Marvelous Mrs. Maisel – all included with Prime Video. Members also enjoy a growing list of unique benefits like Prime Music, Prime Reading, exclusive products and much more. We will keep introducing new ways to make members' lives even better."

The company doesn't disclose the number of Prime members in its earnings. Instead, the company shows revenue from "subscription services," which includes Prime in the U.S. and overseas, as well as subscriptions for things such as e-books and music. In the third quarter of 2017, subscription revenue grew 59 percent from the prior year, to $2.4 billion.

Research firm GBH Insights estimates 88 million people subscribe to Amazon Prime and expects only a 2 percent churn from the price hike as the more expensive monthly rate nudges users to an annual subscription, analyst Daniel Ives said.

Morgan Stanley said in a note published in December that Amazon Prime growth is plateauing in the U.S., showing the first signs of a slowdown. It based its conclusion on a survey of 1,000 U.S. adults.

Amazon shares were up modestly midmorning Friday.

— Reuters contributed to this report.