Basic maths is a major problem for almost 17 million British adults between 16 and 65, campaigners with a new organisation, National Numeracy, have warned.
One in two working-age adults find it difficult to understand easy sums like additions and deductions in their pay slips or basic calculations in everyday life.
Up to 49 percent of the working population have only basic numeracy skills - equal to an 11-year-old - according to a government survey conducted in 2011. The number has grown by two million in the past eight years.
"That's a scary figure, because what it means is they often can't understand deductions on their payslip, they often can't calculate or give change," said Chris Humphries, chairman of National Numeracy.
"They have problems with timetables; they are certainly going to have problems with tax and even with interpreting graphs, charts and metres that are necessary for their jobs. It does matter. Poor numeracy seriously blights an individual's life chances."
Humphries is the former chief executive of the UK Commission for Employment and Skills.
National Numeracy is working to change the "I can't do maths," attitude among Britons, revealed Mike Ellicock, chief executive of National Numeracy.
The organisation is spearheading a national arithmetic campaign to improve the situation.