A Conservative government would reduce the benefit cap to £23,000 a year in a bid to get people on benefits "back into work".
David Cameron made the promise in the latest round of campaigning ahead of the general election in May.
The move would mean the benefit cap would come down from £26,000 ($39,277, €34,935), "within the first few days" of a Tory administration, and would save the Treasury £135m.
The prime minister pledged that the savings would be invested in a scheme to boost apprenticeships.
"This tells you everything you need to know about our values. Conservatives believe we should be giving people the chance of a better future while encouraging people on benefits back into work," Cameron said.
"We want to put people's hard-earned taxes into lifting people up, not holding them down. Over the next five years millions of young people will get a decent start in life, learning a trade, and knowing the purpose and pride that comes with that."
Cameron also said that a further £120m would be gained by ending housing benefit for 18 to 21-year-olds.
But the prime minister has outlined that he would not make cuts to pensioner benefits as "it wouldn't be fair".
"It wouldn't be fair to target pensioners with reductions. It is right to protect pensioners and give people dignity and security in old age, as this government has done," he told BBC Radio 4's Today Programme.
Elsewhere, the Liberal Democrats have published a poster – a parody on the Conservatives' election poster – warning voters not to "take the wrong turn" towards "reckless borrowing" by Labour or "reckless cuts" by the Tories.
The latest poll from YouGov for The Sun put the Tories on 34%, Labour on 33%, the Liberal Democrats on 6%, Ukip on 15% and the Greens on 7%.