Centrebet primary analyst Neil Evans said August 28 was now well ahead of August 21 and the odds for September 4 had also improved.
“I have been told by a Labor source that August 28 is the target date, with September 4 now being ear-marked as the back-up date,” Mr Evans said.
August 28 has firmed from $1.85 to $1.70, while September 4 is $4.25 from $6.
Mr Evans said a prominent lawyer had waged $60,000 for Labor to win at $1.22.
The coalition are at $4.10 to win the next election.
Meanwhile, Geens leader Bob Brown is tipping an August 21 or 28 election.
The election date would be the top priority on Prime Minister Julia Gillard’s agenda at a Tuesday cabinet meeting, Senator Brown said.
“I think either this week or next week she’s likely to go to the governor-general’s office asking for an election,” he told the Nine network on Sunday.
“The Labor strategists who changed the prime minister so readily over the mining tax will now be looking at the best time for the government to go to an election.”
Greens losing ground
The Greens lost ground at the polls after Ms Gillard was installed as leader.
Senator Brown said he put it down to her popularity as Australia’s first female prime minister.
“I raised a glass to that myself, it’s an historic breakthrough,” he said.
“However I think a lot of Green votes went across and parked with Julia and Labor voters came and parked with us.”
Voters did not like the mess Ms Gillard has made of the asylum seeker policy or her discrimination against same-sex couples in marriage laws, Senator Brown said.
The major parties did not realise the importance of climate change and setting a carbon price to voters, he said.
“The big parties are out of kilter with the majority feeling in this country,” he said.
“They need to change and get a carbon price.”
The prime minister could not avoid setting a carbon price and if she did it would disadvantage the opposition, Senator Brown said.
“Tony Abbott will be seen as last century, totally out of touch on this issue,” he said.