Voters will head to the polls in the Victorian seat of Dunkley on Saturday, following the death of Labor MP Peta Murphy.
Mr Dutton said despite the efforts of Liberal candidate Nathan Conroy, he expected a three per cent swing away from the government, which would still leave the seat in their possession.
"Despite Nathan's great efforts and all the work of volunteers six per cent is a tough ask," he told 2GB on Thursday.
"The prime minister is out there saying that the average swing in a by-election is seven per cent, you wouldn't believe it, the prime minister may not be that truthful when he says that figure."
Prime Minister Anthony Albanese, alongside cabinet ministers, have claimed in the days leading up to the vote, that the average swing away from a government is about seven per cent.
Mr Dutton said since the second world war, the average swing against a government in a federal by-election is 3.6 per cent, about half of what Mr Albanese is claiming.
The by-election is seen as 2024's first major litmus test for the government as it heads into an election year.
Treasurer Jim Chalmers said there's been an "influx of rabid right-wing money" used to campaign against Labor in Dunkley.
Right-wing lobby group Advance, which campaigned against the Indigenous voice to parliament, has rolled out billboards and social media ads taking aim at the prime minister over cost of living pressures.
Asked if a loss would be a rejection of the changed tax cuts, Dr Chalmers disagreed, but said it would be really close as by-elections were tough on incumbent governments.
"It's made harder by this influx of rabid right wing-money that we've seen with the Advance campaign," he told the ABC's RN.
"The sorts of advertising that we've seen from that group goes well beyond the acceptable norms of ... sensible Australian politics.
"We don't want to see our politics go down that path, don't want to see this kind of money decide elections and by elections."
Dr Chalmers said his message to voters in Dunkley was to not reward Opposition Leader Peter Dutton for his "nasty negativity or his lack of alternatives".
Polling in the electorate found most people supported Labor's changes to stage three tax cuts, which increased benefits for lower paid workers while decreasing the windfall for higher income earners.
Mr Conroy, the mayor of Frankston City Council, is contesting the seat for the Liberal Party.
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