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.
Millions of pounds have been wiped off the value of Britain's listed retailers amid fears over soaring staff costs from the new national living wage.
Fashion chain Next, Sainsbury's and Debenhams were among the stock market casualties in the second day of share losses for the sector as experts warned they faced significantly higher costs from the plans revealed in yesterday's summer Budget.
Marks & Spencer and Argos owner Home Retail Group were among listed retailers sent as much as 3% lower yesterday after George Osborne unveiled plans for a compulsory "living wage" of £7.20 an hour for over-25s from next year, rising to £9 by 2020.
Next was more than 2% lower in the FTSE 100 Index today, while Sainsbury's fell more than 1% and Debenhams dropped 3% in the FTSE 250.
John Harding, employment tax partner at PricewaterhouseCoopers, said businesses needed to prepare for a "significant increase" in staff costs.
He added: "Although this increase will only affect the over 25s they do make up a significant proportion of employees who are either on or just above the current national minimum wage.
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.