David Cameron has said the decision to remove child benefit from better-off families is "the right approach".
He told BBC One's Andrew Marr Show "85% of families" would get the payments in "exactly the way they do now".
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.
Labour's Ed Balls called the child benefit changes "perverse".
Mr Cameron's comments come ahead of the coalition's mid-term review on Monday.
Changes coming into effect from 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It will be fully withdrawn where one parent earns above £60,000.
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.
"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."
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."
Asked about government plans to cap working age benefits at 1% - including the rise in the pay of public sector workers, out-of-work benefits, and tax credits - Mr Cameron said "those are all in my view absolutely right decisions".
"We need to control public sector pay... we need to limit the growth of welfare payments overall - and that must include the tax credit system, and for those out of work it's right that their incomes aren't going up faster than people in work."
The prime minister also insisted the government was going "full steam ahead" with a packed agenda in the second half of its term.
In the wide-ranging interview, Mr Cameron made a number of major points, including:
- He promised British voters they would be offered a "real choice" on Europe at the next election
- On the economy, he said it was vital for a country to be able to pay its debts - maintaining "a low rate of interest" so it could borrow money cheaply
- He said he was "absolutely determined" to overhaul the deportation system so the radical cleric Abu Qatada and others could be deported from the UK before they appeal
- The prime minister also said he was "absolutely clear" Britain would defend the Falkland Islands in the face of mounting pressure from Argentina
- He also confirmed he wanted to remain prime minister until 2020
Writing in the Mail on Sunday, Chancellor George Osborne said he took "no great pleasure" in reducing people's benefits but that it was needed to ensure a "brighter future".
Conservative Party chairman Grant Shapps told the BBC's World at One: "I have three children I've filled in the form. I totally understand and get how frustrating these things are."
Mr Balls, Labour's shadow chancellor, told Sky News the changes to child benefits were "perverse".
"It's a complete shambles," he said.
"We're going to have many many hundreds of thousands of people who will end end up filing in tax returns because they didn't realise they were supposed to apply by today not to get the child benefit.
"I've always supported a principled approach to the welfare state which we would call progressive universalism."