Millions of shoppers will fail to bag winter sale bargains as they lack basic maths skills, the government says.
Millions are said to struggle to work out sale offers
Ministers want people who find it hard to work out "20% off" or "buy one, get the second half-price" offers to sign up for free refresher maths courses.
Staff from its Get On campaign will be out among the crowds at 10 city centres across England with tips.
The Department for Education and Skills says 14.9m people lack numeracy skills expected of an 11-year-old child.
The Get On campaign staff will be handing out percentage calculators and encouraging shoppers to test themselves to see if they could improve their skills.
"We all use numbers every day, but millions struggle to do the kind of basic sums that are so essential to our lives at work and at home," said Skills Minister Phil Hope.
"Everyone enjoys the hunt for a bargain, but people might not realise that they can brush up their maths or reading and writing - locally, and for free."
Shops across the country are gearing up for one of the busiest days of the year, with some opening up in the early hours of the morning.
But many chains and department stores already began their sales a day ahead of the traditional 27 December start date.