One in four adults has difficulty with mental arithmetic, a survey suggests.
People use maths up to 14 times a day, the survey said
Women are less confident than men, with one in three struggling to add up sums in their head, compared to 18% of men, the poll of 2,000 adults found.
Some 47% of those polled wished they had learnt more maths at school, the survey for numeracy campaign charity Every Child Counts suggested.
And more than half of women asked maths questions by their children or family said they struggled to answer them.
The findings tie in with earlier research that suggests a large chunk of the adult population has problems doing basic maths.
This is problematic as it is estimated that these skills are needed up to 14 times a day.
The survey suggested one in five adults aged 25 to 34 said they felt a greater ability in maths would further them in their career.
Severe difficulties with maths were spread across the social classes.
Some 3% of those working in professional, administrative and managerial jobs and 4% of those in skilled and unskilled manual trades said they struggled with mental maths in shops most of the time.
A third of those in lower social groups polled said they felt uncomfortable in shops some of the time, compared to 25% in the top social groups.
Those aged over 55 were the most confident at 77%, compared to 64% of the 25-34-year-olds who were the least confident.
Adults taking part in the poll were also asked a mathematical question: what is the square root of 64?
One in five did not give the correct answer of eight.
The chairman of charity Every Child a Chance, which is running the campaign, John Griffiths-Jones, said adult innumeracy was one of the greatest scourges facing the country.
"The survey shows how essential it is that the business community gets involved in tackling the problem."
The charity is working with the government to develop a programme helping primary-age children struggling with numeracy.
"Through the programme we aim to find a long-tem solution, spearheading resources of specially trained teachers to help the seven-year-olds who have the greatest difficulties with maths."
The Department for Innovation, Universities and Skills is working on an adult numeracy strategy which is due to be launched later in the year.