Kenyatta received 6,173,433 votes out of a total 12,330,028 ballots cast, while Odinga got 43.31 per cent.
Kenyatta and Odinga camps have raised questions about the vote process, so legal battles could push that date back.
Election officials had said turnout was more than 70 per cent of the 14.3 million eligible voters.
More than 600 people have been killed and about 250,000 people displaced.
Kenya's defeated presidential candidate Odinga has called for a public rally on Wednesday.
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