No one knows what the economy will look like when income tax cuts take effect in 2024, but Malcolm Turnbull is already thinking about bringing them in earlier.
Workers will get hundreds of dollars back in their pockets at tax time next year after the federal government's $144 billion income tax package passed the Senate on Thursday.
The later stages of the tax cuts won't be due until 2022 and 2024, leading to questions about whether Australia will be able to afford them then.
"I would love to think we would be able to bring some of these tax cuts forward if the budget enables it," Mr Turnbull told ABC radio on Friday.
The 63-year-old prime minister, who will be 69 when the final tax cuts are due, said he planned to stay in the job.
"As long as I'm doing a good job, I want to be prime minister," Mr Turnbull told 3AW radio.
But Labor leader Bill Shorten says it was a "complete joke" and irresponsible to give tax cuts so far in advance.
"Can he guarantee that he knows what the economy will be like in seven year's time?" Mr Shorten told reporters in Brisbane.
"If he can't guarantee that, how can he guarantee these tax scales?"
The prime minister says voters have a choice between the government's tax cuts and Labor's policy to deny future cuts to high-income earners at five by-elections on July 28.
Labor has promised to repeal the final stage of the plan if it wins the next election.
Treasurer Scott Morrison said the cuts start with low and middle-income earners from July 1.
"Then over the next seven years, those taxes come down right across the board so that 94 per cent of Australians won't face a marginal tax rate higher than 32.5 cents," Mr Morrison told the Seven Network.
Almost all the Senate crossbenchers supported the tax package, despite objections from Labor and the Greens.
Pauline Hanson's One Nation votes were crucial after she spoke to the government about more support for regional apprentices.
"She's asked the government to consider it, we've agreed to consider it," Finance Minister Mathias Cormann told Sky News.
There was wide support for cutting taxes on people earning up to $90,000 a year, but Labor opposed the 2024 cuts for people earning up to $200,000.
That stage abolishes the 37 per cent tax bracket entirely, reducing the number of tax brackets from four to three and flattening the tax system.