Sri Lanka's election department said on Tuesday the presidential poll would take place between January 11 and February 13, with a final date set to be announced in the next two weeks.
Local media reports have suggested that the election could be held on January 23, a day considered astrologically auspicious for the government.
"We will be in a position to announce a date for the election after accepting the nomination papers in the next two weeks," an official said, adding that the vote could be anytime between January 11 and February 13.
The department will begin accepting nominations within a week from candidates wishing to challenge President Mahinda Rajapakse, who called the snap poll late on Monday.
Rajapakse came to power in November 2005 but plans to cut short his current six-year term.
"The work I should have done during my six-year term has been completed in four," the president said. "Therefore, I have decided to have an early presidential election. I am not afraid to go before the people now."
However, he did not say when the vote will be held.
Sri Lanka's constitution allows the president to call a snap poll after completing four years in office.
The government had been keen to hold early elections to benefit from the defeat of Tamil separatists, who were wiped out in May at the end of a government offensive to bring an end to a decades-long ethnic conflict.
Former army general Sarath Fonseka, who is widely credited with the military strategy that secured victory in May, is expected to stand against Rajapakse.