Recent years have seen online shopping figures consistently peaking on the first Monday in December, probably explained by most UK consumers having just received their last pay cheque before Christmas.
Visa Europe predicts about £320 million will be spent on its cards alone as online transactions top 6.8 million, an increase of 21% on last year, making December 3 the busiest online shopping day in history.
It said: "A combination of pay day for the majority of consumers falling on the last Friday of the month and a weekend spent browsing the shops results in shoppers logging on to buy their gifts online on the subsequent Monday.
"All of these factors will result in consumers spending £222,222 per minute, making 4722 transactions every 60 seconds."
Visa Europe commercial director Dr Steve Perry said: "On Mega Monday, people across the UK will go online and use their Visa cards to make 6.8 million transactions, the most in a single day in UK history. That's 21% more than in 2011, signalling that consumers are becoming increasingly accustomed to the advantages of shopping online for everyday purchases and special items."
Amazon.co.uk also predicts Cyber Monday to be its biggest single day, with orders set to peak at 9.20pm.
Christopher North, managing director of Amazon.co.uk, said: "As people increasingly shop on mobile devices and benefit from fast broadband at home, we're seeing a move towards customers buying their Christmas gifts later in the evening when they are at home relaxing."
Marks & Spencer also said it was prepared for what it expects to be its busiest day of the year.On the equivalent Monday last year, M&S online orders were triple that of an average day, with one placed every second.
The busiest shopping day on the high street often falls two days before Christmas Day, with the weekend of December 22 and 23 expected to draw peak numbers of shoppers this year.