Almost half of adults have maths skills below those needed for the lowest possible GCSE pass grade, a government survey suggests.
One in five adults were below the numeracy standard set for 11 year olds
The Department for Education and Skills blamed "decades of neglect" for figures showing millions of people lacking basic literacy and numeracy skills.
The survey found 47% of the adults in England - or 15 million people - had a lower level of mathematical knowledge than was needed to gain a grade G at GCSE.
Some 21% - or 6.8 million - were less numerate than the standard set for 11 year olds in national tests.
Meanwhile, 16% of adults had sub-GCSE literacy, with 5% failing to achieve the expertise required of 11 year olds.
Skills minister Ivan Lewis said: "I am determined to ensure that today's young people will no longer endure the decades of neglect in literacy and numeracy education which is reflected so starkly in this survey.
"Our recruitment of 50% more maths teachers in just four years and dedicated literacy and numeracy strategies in primary schools are already delivering significant improvements in maths attainment at secondary level."
The DfES said the number of adults with sub-GCSE literacy skills had fallen from 7 million to 5.2 million since 1997.
However, the earlier figure was based on an estimate.
Those adults lacking an 11 year old's accepted standard of numeracy had fallen just by just 200,000.
The DfES findings, based on a survey of 8,730 16 to 65 year olds in England, found a strong link between numeracy and literacy and higher wages.
Some 68% of full-time workers earning more than £20,000 a year had gained at least one GCSE at grade C or above.
Parents with poorer numeracy and literacy were also less confident when helping their children with school work, the DfES found.
The CBI estimates that poor skills cost the British economy £10bn a year.
Liberal Democrat education spokesman Phil Willis said: "Decades of neglect in British education are continuing under Labour.
"After six years in office, the government can no longer blame its discredited predecessor for the shocking lack in the nation's skills.
"The Government's obsession with misguided targets has resulted in minimum improvement at GCSE level."