Previously Scholars believed 563 BC, and now many scholars especially Gombrich has been advancing the idea for the last 30 years that he was born around 480 BC...I personally find it very problematic reconciling the new date with the chronology of Indian Kings with whom Buddha supposedly interacted..but on the other hand, the closer Buddha is to us, less of the supernatural fluff is present ..
Seriously, I think the consensus is that nobody knows exactly.
There's not even a consensus on when he died. Tradition states that it was on the full moon day of May, but from what the Mahāparinibbāna Sutta says, it should have been in January (about three months after the end of the Rains in October), perhaps on the night of the New Moon.
What benefit would it be to know exactly the date of the Bodhisatta's birth?