Cyber Monday sales rise -- but by how much?

This year's Cyber Monday online sales rose over sales from 2013, but the exact increase depends on who you ask.

Online sales for the day were up by 8.5 percent over last year's Cyber Monday, according to IBM's Digital Analytics Benchmark. Mobile sales snagged 22 percent of all online sales, a 27.6 percent jump over last year.

The average online buyer spent $124.21, down 3.5 percent year over year, IBM said. Shoppers bought an average of 4.1 items per order, up 3 percent from last year.

Cyber Monday is a term cooked up by marketers several years ago to convince shoppers to surf the Web the first Monday after Thanksgiving to pick up the latest holiday bargains. Retailers count on holiday shoppers to ring in a healthy portion of overall sales for the year. As such, many online vendors offer huge sales, savings and other discounts to get consumers to spend Monday shopping online.

An 8.1 percent rise in online sales doesn't sound too bad, but it failed to meet expectations. IBM blamed the shortfall on retailers offering online deals weeks in advance, prompting consumers to begin their holiday shopping earlier than usual.

"Consumers are not holding back their purchases for deals on certain days anymore and that trend is becoming increasingly clear," Jay Henderson, strategy program director at IBM, told Reuters.

But wait, a different report says that Cyber Monday sales actually soared by 16 percent from 2013. The 2014 Digital Index Online Shopping report from Adobe pegged online sales for the day at $2.65 billion, a healthy increase over last year.

The top 25 retailers, each of whom snagged $30 million or more on Cyber Monday, boosted online sales by 25 percent for a total of almost $1.8 billion. Smaller retailers who grabbed $2 million or less in sales, saw their take grow by just 5 percent from last year. The biggest discounts popped up in the morning, while 54 percent of holiday spending came outside normal working hours, Adobe said.

"Cyber Monday sales were up 16 percent this year, with the biggest retailers seeing the biggest gains," Tamara Gaffney, principal analyst for the Adobe Digital Index, said in a press release. "The early birds caught the worms on Cyber Monday, with shoppers getting the steepest discounts in the early morning hours."

Okay, so why the difference in numbers between IBM and Adobe?

IBM said that its Digital Analytics Benchmark analyzes millions of real-time transactions across approximately 800 US retail websites.

Adobe explained its process as follows:

The latest findings are based on the analysis of aggregated and anonymous data of more than 400 million visits to 4,500 retail websites on Cyber Monday. Adobe's Online Shopping reports offer the most comprehensive compilation of data in the industry. More than $7 out of $10 spent online with the top 500 US retailers are measured by Adobe Marketing Cloud, more than any other technology company.

So the difference may be a matter of numbers with IBM tracking 800 sites and Adobe looking at 4,500 sites.

IBM spokeswoman Amanda Carl said other organizations may be using different methods, data sets and time frames to calculate their results. She noted that all the findings point to a similar trend in holiday shopping.

"[IBM saw] strong growth for Cyber Monday, which remains the largest online shopping day of the year," Carl said. "In addition, we're reporting nearly 13 percent overall growth for the five-day Cyber Week period between Thanksgiving and Cyber Monday, which includes 17 percent online growth during the Saturday and Sunday after Thanksgiving. I think the trend we're seeing is that online holiday shopping is less concentrated on a single day and more spread out over the five-day span."