RESTON, VA: As the US holiday sales season kicks off with Thanksgiving and Black Friday, a new report forecasts that shoppers will spend $70.1bn online in November and December.

That represents year-on-year growth of 14%, according to research firm comScore, which also expects Cyber Monday, the first Monday after Thanksgiving, to top more than $3bn in online sales to make it "the heaviest online spending day in history for the sixth straight year".

Spending via desktop computers is expected to reach $58.3bn, far exceeding the $11.7bn forecast to be spent via mobile, but a key finding in the report is the rapid growth of mobile compared with last year.

Mobile digital commerce over the holiday season is projected to be 47% higher than in 2014 and that compares with year-on-year growth of just 9% for desktop. Overall, digital is expected to account for about 15% of consumers' discretionary spending.

Gian Fulgoni, executive chairman emeritus of comScore, said that analysis of last year's spending habits showed that online shopping more than compensated for reduced spend at physical stores and he predicted this would be repeated.

"Last year, many retailers opened stores on Thanksgiving Day with unexpected results, as some consumers shifted their store visits from Black Friday to Thanksgiving Day but reduced their spending rate," he said.

"The good news is that online buying more than compensated for the softness of in-store sales, with growth rates of more than 25% during those two days. We anticipate that happening again this year."

He added that the overall economic outlook remains positive for consumers and retailers, who will benefit from an additional shopping day between Thanksgiving and Christmas as well as from low gas prices that will give consumers more ready money to spend.

Other recent reports have also offered good news for retailers. Forrester Research predicted earlier this month that US online holiday sales will top $95bn in 2015 while the Deloitte 2015 Holiday Survey found consumers plan to spend an average of $1,462 in 2015, up from $1,299 in 2014.

Data sourced from comScore, Forrester, Deloitte; additional content by Warc staff