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.
The Chancellor has been accused of an "outrageous" tax hike on motorists that will lead to more uninsured drivers on the country's roads.
George Osborne raised the Insurance Premium Tax in yesterday's Budget from 6% to 9.5%, a move which the AA said could backfire.
"Drivers shouldn’t be dancing in the streets or at the pumps due to a promised freeze in fuel duty," said Edmund King, AA president.
"The sting is in the tail. The Insurance Premium Tax increase on the average car insurance policy is still equivalent to a fuel duty increase of almost 2p per litre. Either way drivers are being hit in their pockets.
"This is an outrageous hike which could well backfire by leading to an increase in uninsured drivers"
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.