Nearly complete results from Tuesday's election show Mr. Bush leading Mr. Kerry in the popular vote by 51 to 48%, or about 3.5 million votes.
Delaying the concession was a dispute about the outcome in Ohio. President Bush is currently ahead by about 140,000 popular votes. But an estimated 150,000 to 250,000 votes there remain to be counted, and the Kerry campaign had said it wants every vote counted.
Voter turnout was heavy after a long and heated campaign focused on the war on terrorism, Iraq and the economy. But many exit polls suggest Bush supporters were swayed by the president's stance on what were termed "moral issues," including a ban on gay marriage and opposition to stem cell research.
Mr. Bush did best in the South and West of the country. Mr. Kerry was strongest in the Northeast, Midwest and West Coast.