The Liberal-National coalition is on track to topple Labor after six years in opposition, as Tony Abbott pledges to be a leader for all Australians.
Opinion polls suggest the coalition could make a net gain of about 15 seats, taking its numbers to 87 in the 150-member House of Representatives.
A day before he could become prime minister, the opposition leader was optimistic.
"A successful national leader understands that you've got to be a leader for everyone, even the people who don't necessarily support you, even the people who won't ever vote for you," Mr Abbott said on Friday.
"You've got to treat them with respect."
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Mr Rudd, however, insisted Labor was still in with a chance of winning.
"There is fight in the old dog yet," Mr Rudd said at a union rally on the NSW Central Coast.
"I believe we can do it. This is not wishful thinking, it's a matter of looking at the maths."
The prime minister said the vote gap between the two major parties was "somewhere between 300,000 and 400,000 Australians who we need to get on our side of the pile".
Mr Rudd, who was recruited back into the Labor leadership in June in a bid to save the government, declined to talk about his future should his party lose.
"I won't engage in hypothetical land," he said.
Education Minister Bill Shorten, who is being tipped as a Labor leadership contender, said he did not regret backing Mr Rudd's return to the top job.
"I believe that people had completely switched off listening to Labor," Mr Shorten said of the party under former leader Julia Gillard.
"Kevin Rudd had certainly helped contribute to making us competitive."
Former prime minister John Howard, who has played a considerable role in the Liberal campaign, said he was most nervous about the drift to minor parties.
An Essential poll taken this week put the Greens' national support at 10 per cent and "others", including the parties led by veteran MP Bob Katter and billionaire Clive Palmer, at 12 per cent.
Liberal frontbencher, Senator Arthur Sinodinos, said he did not think the coalition would win control of the Senate because of the expected vote for minor parties.
Greens senator Sarah Hanson-Young declared Mr Abbott would win the election, which was why the Senate vote would be crucial.
"We've got to make sure he (Tony Abbott) doesn't get absolute power. This is the challenge," she said.
A record 14.7 million people have enrolled to vote.
More than three million people are expected to vote early, with the figure at a record 2.8 million by 1pm on Friday.
More than 1700 candidates and 54 parties are in the running for 40 seats in the Senate and 150 seats in the House of Representatives.
Every major daily newspaper except Melbourne's The Age ran editorials in favour of Mr Abbott.
The final Fairfax/Nielsen poll, released on Friday night, put the coalition on track to win 54 per cent of the vote to Labor's 46 per cent.
The poll of 1431 voters was taken on Wednesday and Thursday.
