Clinton, who lost the Democratic presidential nomination to Barack Obama in 2008, is widely expected to make another run for the White House in the upcoming vote.
"I will be making a decision around probably after the first of the year about whether I am going to run again or not," the former first lady said in Mexico City at a forum hosted by the Telmex Foundation of Mexican billionaire Carlos Slim.
"It's a very serious undertaking so obviously I'm thinking about it, but I have not made a decision yet," she said.