Australia won't know the results of the same-sex marriage survey until 10am on Wednesday morning. But there has been a growing assumption over the course of the campaign that the "yes" camp will win.
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Senior ministers such as Peter Dutton and Julie Bishop have said they think the "yes" vote will win. "Yes" campaigner Sarah Hanson-Young has said she's "very, very confident". And as voting closed last week, "no" spokesman Lyle Shelton conceded, "we're chasing down a big lead".
Poll after poll has also found support for same-sex marriage is at about two to one. Just before the survey closed last week, a Guardian Essential Poll found 64 per cent of people who voted say they ticked "yes". As pollster John Stirton recently told Fairfax Media, "it's very hard to see how the 'no' case could win from here unless an awful lot of people are straight-out lying to pollsters".
But is a "yes" result the sure bet people think it is?
Earlier this month, Griffith University researchers suggested there could be a narrow "no" victory, based on an analysis of Australian tweets about same-sex marriage posted last month. The researchers used a similar method to accurately predict the last US presidential election, Brexit vote and Australia's 2016 federal election.
"People don't always say what they really think [to pollsters]," Big Data and Smart Analytics Lab researcher David Tuffley says. "On social media, people can often be a little more candid."
With almost 80 per cent of eligible voters having returned their forms at the last count, Tuffley says the final result is "too close to call".
So what happens if a majority of Australian voters have opted for "no"?
From the Coalition's perspective, it would mean same-sex marriage was off the table for the forseeable future.
"It's very straightforward, if there is a 'yes' vote, then we'll facilitate a private member's bill to legalise same-sex marriage, and if there's a 'no' vote, we won't, that's it," Prime Minister Malcolm Turnbull said in September.
"If the people have spoken against it, we won't be proposing it at the next election I can assure you."
One Liberal MP confirmed a "no" vote would end any attempts within the Liberal Party for reform, "it's dead, it's done". While it would still technically be possible for backbench government MPs to cross the floor and bring on a parliamentary vote, there would be enormous party pressure not to. Bear in mind, the renegade group threatening to do this did not go through with their plan several months ago, when arguably, it was politically easier to do so.
As another government MP noted, given the high response rate to the postal survey, it will be hard to argue the final result is illegitimate.
So the ball would be in Labor's court. Even if there is a "no" result, Labor (who has opposed the idea of a public vote) is holding to its pledge to introduce a bill to legalise same-sex marriage if it wins the next election. Labor sources say while the party would "cop some heat" by pushing ahead with its plans, there is no chance of winding back the policy.
At the last ALP national conference in 2015, the party decided to bind all MPs to a "yes" vote in Parliament after the next election. While there are some MPs, such as Victorian senator Jacinta Collins, who are known to support the existing definition of marriage, "no" supporters within Labor ranks are an ever-diminishing group. And have been noticeably quiet during the postal vote campaign.
But even so, the Labor option means waiting until next year or the year after whenever a federal election is called – for a parliamentary vote. And of course, it depends on a Labor victory and any future Senate having the numbers to pass a bill as well.
Marriage equality advocates caution that if there is a "no" result, the first thing needed will be support for LGBTI people and their families. Many jokes have been made during the campaign by gay people who say they will have to move countries if "no" wins. It's unlikely the LGBTI community will see the funny side if the majority of voters reject the idea of same-sex marriage.
"For us this isn't about political games. It's about our humanity at the deepest level, so many LGBTI people will feel devastated," says long-time gay rights advocate Rodney Croome.
Support services, such as the youth-focused organisation, ReachOut, are preparing for a spike in demand in the coming months, regardless of the result.
Another scenario that has not been given much public thought is: what happens if the vote is very close, making it hard for either side to claim a mandate.
The positioning is already starting on this front, with Tony Abbott last week saying any "no" vote of 40 per cent would be a "moral victory". A close vote, with a narrow "yes" victory would give an added boost to the growing push among conservative Liberal MPs to include multiple exemptions in any same-sex marriage bill to favour those who don't support the reform.
"There are issues with a non-emphatic 'yes' vote," says Croome. "It gets messy."
The "yes" campaign has booked DJs and food stalls for events to coincide with the announcement on Wednesday. But if there is a surprise "no" result, it will not be the end of the campaign for same-sex marriage.
"If it is a no, it will be a tough day," says "yes" spokesman, Alex Greenwich. But he adds the movement has suffered big setbacks in the past – such as bills being defeated or not even coming to a vote – and has then regrouped.
"You never stop wanting to be treated as an equal citizen."
