About $3.38 trillion worth of online merchandise will be abandoned in online shopping carts this year. Here's a look at the reasons for shopping-cart abandonment, and also some tips for preventing it.

Some "21% of consumers cite time constraints as a common reason for cart abandonment," states Ripen Ecommerce. To prevent that issue, "include a guest checkout option so shoppers aren't forced to make a new account," Ripen suggests.

Also, 44% of shoppers will abandon a cart because shipping costs are too high. "Offer free shipping with a minimum threshold slightly higher than your average order value," suggests Ripen.

And 75% say they plan to return to a site or go to a store to complete a purchase. "Use inventory counters and/or limited time offers to compel shoppers to complete a sale," Ripen recommends.