Since a change to its media ownership regulations in 1999 that counted television station ownership maximums by a national market percentage rather than by the number of stations that could be allowed in their portfolio, FCC rules mandate that the total number of television stations owned by any company can only reach a maximum of 39% of all markets in the U.S. Until 2016, a "discount" allowed a broadcaster to cover up to 78% of the U.S. with UHF signals; this loophole was closed in 2016, although existing companies above the 39% threshold will be covered under a grandfather clause and, although they will not be allowed to acquire any more stations, they will also not be forced to sell their existing portfolios.