Thirteen million families will lose an average of £260 each year because of the change to working-age benefits, the Institute for Fiscal Studies (IFS) has said.
Reacting to the first all-Conservative Budget in 19 years, the IFS said it was "regressive" and had taken "much more" from the poor than the rich.
George Osborne earlier defended his Budget, saying it represented a "new contract" for Britain.
It is fair to say Iain Duncan Smith liked the announcement of a new National Living Wage.
The Work and Pensions Secretary punched the air wildly and shouted "get in" as George Osborne confirmed the move.
Unsurprisingly, the animated response was picked up on Twitter.
Since the Budget, a cascade of analysis has crashed across our screens and squirted ink over our newspapers - much of it missing the point.
This afternoon, the Institute for Fiscal Studies presented a damning analysis of George Osborne's Budget. Here we explain the key points.
The Chancellor's "Living Wage" is considerably lower than the rate the Living Wage Foundation campaigns for but this is still a bold move.