The claim: Boris Johnson unexpectedly unveiled the Conservatives' plan to raise the threshold at which people start paying National Insurance contributions. He said: "If we're lucky enough to be elected, so the first Budget we will go up to the £9,500 threshold and that will, as I say, put £500 into the pockets of everybody."
Reality Check verdict: That's not the correct figure. The Conservatives' own press release says the benefit from raising the threshold to £9,500 in 2020-21 would be £100 per year. The Institute for Fiscal Studies (IFS) says it would be £85 per year.
National Insurance contributions (NICs) are a tax of 12% taken off UK workers' salaries above a certain level, currently £8,632. Self-employed people pay them too.
On a visit to North Yorkshire, the prime minister revealed that the Conservatives plan to raise that limit to £9,500 next year (2020-21).
He told the BBC that this would put £500 "into the pockets of everybody".
But the Conservatives' press release says the move "will cut taxes for 31 million workers by approximately £100 a year".
The IFS has a slightly different figure - it calculates that everyone earning more than £9,500 would benefit by £85 in 2020-21. Their figure is different largely because the threshold would have risen slightly by then anyway to allow for inflation.
It's also worth pointing out that not "everybody" would be affected. People earning under £8,632 and those above the state pension age would not benefit as they do not pay National Insurance.
Mr Johnson has "an ambition" to raise the threshold further to £12,500 and says there would be a timescale announced at the next budget, should the Conservatives get re-elected.
The Conservatives' press release says: "Over time we will raise the threshold to £12,500, saving workers approximately £500 a year".
In a separate interview with ITV News, Mr Johnson talked about the benefit from raising the threshold to £9,500 saying: "It's about £500 a year." The reporter challenged him saying: "That's not what you are guaranteeing. You are guaranteeing about £100 next year and there's an ambition for £500."
But Mr Johnson was adamant: "You are not right there. We are going to £9,500 threshold initially and then the ambition is to get to the £12,500 threshold. But the initial cut that we are making does offer a £500 cut for every working person."