10 Perks of Amazon Prime You Could Be Wasting

Introduced 11 years ago, Amazon's Prime service has grown by leaps and bounds, with an estimated 40 to 50 million members worldwide in 2015, according to analysts. The program, which costs $99 a year and offers members free two-day shipping on an unlimited number of orders for a flat annual fee, has also steadily added perks throughout the years, to a point where some members may be unaware of all the benefits the Prime membership fee has bought them. Here's a rundown of 10 lesser-known advantages of being a Prime customer.

Related: Don't Miss These 13 Perks of Costco or Sam's Club Membership

Even seasoned Prime members may be unaware that another adult living in the same household can be added to the membership and access many of the benefits from their own account. One catch: Payment must be made from the authorizing member's credit card. That may be no big deal if the benefits are shared with spouse or partner, but it could get a bit dicey with, say, a roommate.

That's right, unlimited. And there are free apps available to help upload photos to the cloud. Members also get 5 GB of storage space for videos and other files. Prime members who have run out of room on other cloud storage services -- or don't have a backup at all -- can breath a sigh of relief.

Free two-day shipping is the most talked about benefit of Amazon Prime, but members also have the option of free same-day delivery in select locations (a growing list). There is a $35 minimum order.

Amazon promises free two-hour delivery from local stores and restaurants through Prime Now, within eligible ZIP codes. The offerings include household items and groceries.

Amazon gives Prime members an early crack at its limited-time "Lightning Deals" -- 30 minutes before the general public. Lightning Deals are good only while supplies last, so this could mean the difference between scoring a deal and missing out.

Prime members with babies or toddlers can save up to 20 percent on diapers through Amazon Family when they set up the Subscribe & Save option (which can be canceled or changed).

Prime members get a discount on Amazon FreeTime Unlimited, a service that offers books, movies, shows, apps, and games designed for kids 3 to 12, with no ads or in-app purchases. Prime members pay $3 a month, a 40 discount from the standard $5 fee.

Prime members (and anyone who shares the membership) can borrow a book a month for free from the Kindle Lending Library. But the book must be read on an Amazon Kindle Reader, Fire Tablet, or Fire Phone, not just a device with the Kindle app. Prime members are also automatically registered for Kindle First, allowing them to download and read select titles a month before the release date for free or at a reduced rate.

With Prime Pantry, members can have a 45-pound box of grocery and household items delivered for $6. Weekly deals and discounts can increase savings. But shoppers won't find the giant sizes available at big-box retailers such as Costco or Sam's Club. Rather, the focus is on regular sizes -- a good deal for urban dwellers without a car or extra pantry space.

July 12 marked the second annual Prime Day, when Amazon offers exclusive deals for Prime members only. Although more shoppers were eligible this year, it appears that fewer sought out the thousands of available deals. Hitwise reports an estimated 81.6 million visits to Amazon on Prime Day 2016, down from 86.3 million in 2015.