Area code 403 is a telephone area code in the Canadian province of Alberta, encompassing the southern half of the province, including the Calgary area. It is one of the original 86 area codes assigned in 1947 in the contiguous United States and the then nine province extent of Canada.

Prior to October 21 1997, the 403 area code encompassed the whole province of Alberta, the Yukon and the western half of the Northwest Territories, reaching more than one ninth of the circumference of the planet from the 49th Parallel to the North Pole. The territories were given their own separate area code, 867, in 1997. In 1999, the northern half of Alberta was split into the new area code 780.

Optional provincewide 10-digit dialing began on June 23, 2008 and became mandatory on September 12, 2008. This change was done to accommodate new area codes that have been assigned to the province for future use. On September 20, 2008, Telus Mobility began assigning area code 587 numbers to new customers in the Calgary/Edmonton area.