The Australian Bureau of Statistics revealed on Tuesday that 10 million citizens have had their say, with 62.5 per cent of the voting papers received.
"I've already voted 'no' and I'd encourage people to do the same but it's a democratic process," Mr Dutton told 2GB radio on Thursday.
"My sense of where the debate is at is that the 'yes' vote will get up."
Despite being personally against changing the law, the minister has pledged to vote for same-sex marriage in parliament if the "yes" vote wins.
He has had discussions with former prime minister John Howard over religious freedom protections and the pair share concerns.
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"If there is a 'yes' vote then there will be a bill before the parliament, and my argument and others have argued that there should be adequate protections in there," he said.
Treasurer Scott Morrison, who also supports traditional marriage, said he would wait to see the results.
"I mean, Australians are having their say at the moment. That's what I wanted them to have," he told ABC TV.
There are still four weeks to go before the postal survey closes on November 7.
