Shoppers are set to break away from Christmas festivities to spend well over £700 million online today.
Record numbers of consumers are expected to spend "a significant proportion" of their Christmas Day shopping online, either to take advantage of the sales or return unwanted gifts.
They will spend £728 million, up 11% on last year's £658 million, according to data firm Experian and online retailing trade association IMRG.
Experian spokesman Nick Jones said: "We have already witnessed record-breaking spending over the festive period. On Black Friday to Cyber Monday weekend, spending reached a phenomenal £3.3 billion across the four days.
"Though the post-Christmas sales period might not reach these heights, retailers are certainly in for more bumper sales as consumers look to take advantage of further Christmas offers.
"On Boxing Day alone a huge £856 million is expected to be spent, up 22% on last year. In addition, rightly or wrongly, we've seen more people than ever spending a significant proportion of their Christmas Day shopping online.
"Due to the rise of the use of personal connected devices, consumers can now shop for bargains on their mobile or tablet when they have a spare couple of minutes - even if that does mean sneaking away from the festivities and risking the wrath of family members."
A survey for Barclaycard found that 32% of those planning to shop on Christmas Day are motivated by the fear of missing out on the best bargains, 18% expected to be bored and wanting something to do and 15% expected to be disappointed with their presents and wanting to buy replacements.
Some 15% of those planning to shop in the sales expected to do so on Christmas Day, the poll found.
Sales began in earnest online from Christmas Eve, but analysts have raised doubts about their impact on consumers who have enjoyed a steady diet of discounting since the week before Black Friday.
Clothing retailers have been impacted by what is shaping up to be the warmest December in 70 years, while Black Friday in November led a number of high street chains to begin sales early, such as H&M, Gap and Jack Wills.
However figures from VoucherCodes.co.uk and the Centre for Retail Research suggest 22 million shoppers are set to spend £3.74 billion in the Boxing Day sales - a 6% increase on last year.
In good news for the high street, the research predicts that 78% of Boxing Day transactions will take place in bricks and mortar stores.
Online sales are set to be up 13% on last year.
VoucherCodes managing director Claire Davenport said: "While pre-Christmas sale dates have soared in popularity over the last couple of years, it seems they are yet to take over our more traditional savings days, with many retailers choosing to go all out on Boxing Day, running deals as early as Christmas Day right through to the start of the new year.
"Judging from our research, it looks as though consumer appetite to snap up deals is here to stay, both on the high street and online."