Australians have already made up their minds who they will vote for and the coalition's costings will make no difference to the outcome, former treasurer Peter Costello says.

"I don't think it's going to swing votes one way or another," he told the Nine Network.

"People are going to decide, really, on whether they think this government's been a good government or a bad government, they'll have an overall impression of it, most people have made up their minds and I don't think they'll be worrying too much about costings in the last 24 hours."

Mr Costello said the coalition was likely to win by a substantial margin, with the loss of seats in Queensland, western Sydney, Melbourne and possibly even Tasmania.

"Those areas on the east coast where Labor's been strong, I think the Citadel's going to fall and I think the swing is on and it's on all across the whole eastern seaboard including Tasmania."

Mr Costello said it didn't take long for the public to realise that Labor under Kevin Rudd was the same government as under Julia Gillard and therefore they were going to pass the same judgment.