Great question! There used to be, and then a couple of months ago I took it out. One of the users posted a link to a NYTimes article (http://www.nytimes.com/2016/07/04/business/amazon-is-quietly-eliminating-list-prices.html) that describes Amazon's decision to phase out the concept of a "list price" for its products, which makes the concept of %off obsolete as well. Even though you will notice that some products still show up as being some %off their list price, attempting to sort by that value will also include products whose list price is not specified, which make such sort nonsensical. I also used to have a slider that would allow you to only see products that are at least some % off in the search results, but I took it out as well. I think Amazon removed the sidebar filter for %off too. Thank you for writing!