Christmas is celebrated in the United States on the 25th of December. Christmas is a civil holiday and is celebrated by an increasing number of non-Christians, and is an integral part of the holiday season. Christmas is typically the largest economic stimulus for many nations around the world as sales increase dramatically in almost all retail areas. The United States' retail industry generated over three trillion U.S. dollars during the holidays in 2013. These holiday sales reflected about 19.2 percent of the retail industries total sales that year. The Christmas shopping season can start as early as September and some consumers begin even earlier. The economic impact of Christmas is a factor that has grown steadily throughout the United States and the world and will continue to be a significant event and key sales period for retailers and businesses.