The stalemate between Ashraf Ghani and Abdullah Abdullah since the June 14 vote has plunged Afghanistan into a political crisis as US-led NATO troops end their 13-year war against the Taliban.
Both men claim to have won the fraud-tainted election, and the United Nations and the United States have pushed hard for a "national unity government" to try to avoid a return to the ethnic divisions of the 1990s civil war.
"The IEC will officially announce the final result of the presidential election tomorrow," Independent Election Commission spokesman Noor Mohammad Noor told AFP.
"They are set to meet again shortly today to reach a final agreement," he said. "The IEC is not supposed to announce the final results before the agreement is finalised."
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Ghani's campaign team was not immediately available to comment, but said it would issue an update on negotiations later today.
The election process has been plagued by delays and setbacks, and the latest timetable could still change if disputes flare up again over how the new government would take shape.
Ghani - who won the vote according to preliminary results - is set to emerge as president, with Abdullah nominating who will fill the new post of "chief executive officer", possibly taking on the role himself.
President Hamid Karzai, whose successor was originally due to be inaugurated on August 2, was constitutionally barred from standing for a third term in office. He has stayed publicly neutral in the election.
About 41,000 NATO troops remain in Afghanistan, down from a peak of 150,000 in 2010, fighting along Afghan soldiers and police against the fierce Taliban insurgency.
NATO's combat mission will end in December, with a follow-on force of about 12,000 troops likely to stay into 2015 on training and support duties.