Systems and methods for online shopping cart management are provided. According to an embodiment, a shopping cart system receives cart information for one or more items selected by a user on a plurality of merchant websites. The shopping cart system determines related items among the one or more items to populate different carts of the user. In response to receiving a checkout request for a cart containing an item related to other items, the shopping cart system provides an option to check out the other related items. The user may initiate, and the shopping cart system may process, a payment request for items in the checked-out cart. In some embodiments, the shopping cart system may remove items similar to the purchased items from the remaining carts. In further embodiments, the shopping cart system may automatically check out one of the carts after a predetermined amount of time.