Nearly a third of the population of Britain is living on an "inadequate" income, according to research by the Joseph Rowntree Foundation (JRF).
In 2014-15, it said that 19 million people were living on less than the Minimum Income Standard (MIS).
It said the problem was that household costs have been rising, while incomes have stagnated.
The government has already promised to tackle the issue, after Theresa May identified those "just about managing".
It said it was taking "targeted action" to raise incomes.
The MIS is set by experts at Loughborough University, and is based on what members of the public think is a reasonable income to live on.