Video report by ITV News Political Correspondent Paul Brand
Boris Johnson has said he will initially raise the National Insurance threshold to £9,500 and the "ambition is to get to £12,500."
Speaking to ITV News, he clarified the government's position on National Insurance contributions.
"We are going to £9,500 threshold initially and then the ambition is to get to £12,500 threshold, but the initial cut that we are making does offer a £500 cut for every working person," Mr Johnson told ITV New Political Correspondent Paul Brand.
However this was at odds to an earlier pledge the prime minister had made during a campaign visit to an engineering company in Teesside, when he promised to cut National Insurance up to £12,000.
He replied: "I mean low tax for people of the working people.
"We are going to be cutting national insurance up to £12,000, we are going to be making sure that we cut business rates for small businesses. We are cutting tax for working people."
Currently workers start paying National Insurance contributions once they earn £8,628 a year.
Mr Johnson told ITV News he wanted to help those "who are affected by the cost of living."
"The reason we are doing that, I am a tax cutter, I want to do everything I possibly can, but we have to operate within fiscal prudence and we have got to target those who would most benefit and who are affected by the cost of living," the prime minister added.
Speaking in Teesside, Mr Johnson said Labour's plans would impose a "£2,400 "tax burden" on every family in the country.
He said Jeremy Corbyn had voted in Parliament for tax rises of £7,800 on working families.
"They always say they're going to point the finger at billionaires, or whatever, but in the end it's everybody who pays," he said, "because the problem with socialism is that you always run out of other people's money."
Mr Johnson was also challenged to guarantee he would never sell off the NHS, to which he replied: "I can - and I was amazed by what (Jeremy Corbyn) had to say. It's a complete invention."
He said a Labour government would seek to rebalance the economy, giving workers more a say in running the companies they work for.
The PM said the NHS is "one of the greatest contributions this country has made to the world" before adding: "Under no circumstances will the NHS be for sale, be on the table in any trade negotiation we do with anybody."
"I asked him nine times, I did not get an answer, and frankly I do not see how you can lead this country if you cannot answer a very simple question - what side are you going to be on in a referendum on whether to leave or remain in the EU."