Poor numeracy is blighting Britain's economic performance and ruining lives, says a new charity launched to champion better maths skills.
The group, National Numeracy, says millions of people struggle to understand a payslip or a train timetable, or pay a household bill.
It wants to challenge a mindset which views poor numeracy as a "badge of honour".
It aims to emulate the success of the National Literacy Trust.
This has helped improve reading and writing standards since it was set up nearly 20 years ago.
Government figures show almost half the working population of England have only primary school maths skills.
National Numeracy quotes from research suggesting weak maths skills are linked with an array of poor life outcomes such as prison, unemployment, exclusion from school, poverty and long-term illness.
A YouGov poll for the charity suggests that while four out of five people would be embarrassed to confess to poor literacy skills, just over half would feel the same about admitting poor maths skills.
Chris Humphries, chairman of National Numeracy and a former chief executive of the UK Commission for Employment and Skills, said: "It is simply inexcusable for anyone to say: 'I can't do maths.' It is a peculiarly British disease which we aim to eradicate.
"It doesn't happen in other parts of the world. With encouragement and good teaching, everyone can improve their numeracy."
Mr Humphries said just 15% of Britons studied maths after the age of 16, compared with 50-100% in most developed nations.
He pointed toresearch by KPMG auditorssuggesting that annual costs to the public purse arising from a failure to master basic numeracy skills amounted to £2.4bn.
"We are paying for this in our science, technology and engineering industries, but also in people's own ability to earn funds and manage their lives," he told BBC Radio 4's Today programme.
Many people could not get jobs because they struggled to read graphs and interpret documents, while plumbers unable to do the calculations required to install an energy-efficient boiler might lose income, he suggested.
BT chairman Sir Mike Rake, a supporter of the new organisation, said: "Poor numeracy is the hidden problem that blights the UK economy and ruins individuals' chances in life."
Last year's Skills for Life survey suggested that the National Literacy Trust's drive to improve literacy was working, with almost six out of 10 people in England having strong reading and writing skills.
But the same figures also suggested that high-level maths skills in England were declining.
Only 22% of people have strong enough maths skills to get a good GCSE in the subject - down from 26% when the survey was last carried out in 2003.
TV presenter Carol Vorderman, head of the Conservative Party's "maths task force", told BBC News she was "horrified" by more evidence of Britain's poor maths skills.
"I think it is shameful that the system has allowed this to happen... The curriculum needs looking at. GCSEs need looking at. The whole thing, root and branch, needs changing", she said.
Ms Vorderman added that the media bore some responsibility for Britain's negative attitude to maths.
"Obviously with doing Countdown for all those years, people would talk to me about maths. I can't remember a single television programme which I appeared on as a guest where the host has said: 'Oh yes I am really good at maths'... everybody always says they are rubbish at maths."
A spokeswoman for the Department for Education said: "We want the vast majority of young people to study maths up to 18 within a decade to meet the growing demand for employees with high-level and intermediate maths skills.
"We are undertaking a root-and-branch review of how maths is taught in schools, attracting the best maths graduates into the profession."