Voting for the same-sex marriage postal survey closed on Tuesday afternoon, with 12.6 million people taking part.
The figure accounts for 78.5 per cent of Australians eligible to vote.
Voting closed at 4.30pm AEDT on Tuesday.
"We know many Australians like to work to a deadline - well that deadline has well and truly arrived," Alex Greenwich, a spokesman for the Equality Campaign said.
Most opinion polls show the Yes vote will win with around 60 per cent, but an academic study of Twitter opinions refutes that.
A Guardian Essential poll released today showed that of those polled, 64 per cent voted ‘Yes’ in the survey.
Thirty-one per cent were 'no' voters and five per cent declined to answer.
