David Cameron has said the decision to remove child benefit from better-off families is "the right approach".
He added he was also committed to same sex marriage and protecting spending on aid for developing countries.
He told BBC One's Andrew Marr Show "85% of families" would get the payments in "exactly the way they do now".
Both policies have irritated some on the Conservative backbenches.
The prime minister also said the government was "absolutely right" to limit most working age benefits to a 1% rise, which will be the subject of a Commons vote on Tuesday.
But Mr Cameron told the Sunday Telegraph "this is an enormous reform agenda" and urged critics in his own party to "stop complaining."
His comments come ahead of the coalition's mid-term review on Monday.
He added he wanted to "win back" disaffected Tory supporters who had left the party.
Changes coming into effect from Monday will see families with one parent earning more than £50,000 lose part of their child benefit.
'Right direction'
It will be fully withdrawn where one parent earns above £60,000.
He also said he hoped to stay on as prime minister until 2020, telling the Sunday Telegraph: "I want to fight the next election, win the next election and serve - that is what I want to do."
Defending the policy, Mr Cameron said: "I'm not saying those people are rich, but I think it is right that they make a contribution.
Mr Cameron said: "In mid-term in government you are taking difficult decisions. There's always going to be a tendency for people to look at protest.
"This will raise £2bn a year. If we don't raise that £2bn from that group of people - the better off 15% in the country - we would have to find someone else to take it from."
"I don't think my job is to try to identify different segments of people who are going this way or that. My job is to steer the ship in the right direction."
He added: "I think people see it as fundamentally fair that if there is someone in the household earning over £60,000 you don't get child benefit... I think it is the right approach."
Changes coming into effect on Monday will see families with one parent earning more than £50,000 lose part of their child benefit. It will be fully withdrawn where one parent earns above £60,000.
Ministers have said the changes are needed to help the government's deficit reduction plan.
Saying it was a "very difficult" thing to do, Mr Cameron said: "I have complete understanding for people who are having their family budgets changed and money taken away and if there is more we can do to make it easier for people, yes of course."
He said the coalition could have promoted its same-sex marriage reforms better.
"One of things we haven't got across properly is this is what is going to happen in the register office," he said. "We're not changing what happens in church or synagogue or mosque."
Mr Cameron, who is due to make a major speech on Europe later this month, added: "Britain has a role in Europe ... but we're not happy with the way the relationship works at the moment and so we want change."
Mr Cameron and Deputy Prime Minister Nick Clegg will set out their top priorities for the rest of their term - which could take them through until a general election in May 2015 - on Monday.
Their review is expected to include details of a cap on social care costs in England as well as child care and pension reforms.
BBC political correspondent Chris Mason said the leaders wanted to emphasise the government is doing more than just driving down the deficit and will also highlight changes to the benefits system and reforms to schools in England.
Labour's vice chairman Michael Dugher said: "Another year, another relaunch and still none of the change that David Cameron and Nick Clegg promised. They said they'd fix the economy. But living standards are still falling for the hard-working majority...
"Families who put their trust in David Cameron and Nick Clegg's promises of change will be bitterly disappointed to see that another relaunch is all they are offering."
