Nearly half, or 45.7%, of surveyed online retailers will end standard shipping promotions by Monday, according to a poll of 40 merchants from Shop.org, the e-commerce arm of the National Retail Federation trade group. An additional 17.1% will offer their standard shipping promotions until Dec. 18; 17.1% until Dec. 19; 14.3% until Dec. 20; and 5.7% until Dec. 22, according to the report released today.

Shop.org bases its findings on a survey conducted by BIGinsight between Sept. 25 and Oct. 11.

The survey also finds that 85.7% of those 40 respondents will offer express two-day shipping until Dec. 21, with 14.3% offering that delivery option until Dec. 22, the Saturday before Christmas. Meanwhile, 35.5% of the online retailers who responded to the survey said they will offer express one-day or overnight shipping until Dec. 21, with 51.6% going until Dec. 22 and 12.9% until Dec. 23.

“Even after weeks of record-level online traffic to their sites, retailers are well aware that millions of their customers will still shop at the very last minute, regardless of how early they may have started their shopping this year,” says Shop.org executive director Vicki Cantrell. “For some procrastinators, express and standard free shipping offers could be the deciding factor in whether or not they purchase something. In anticipation, retailers will save some of the best deals of the year for the final stretch to reel in the countless last-minute holiday shoppers we see each year.”

A late-season holiday shopping boost could take place on Monday, during an online retail marketing event called Free Shipping Day. More than 1,000 merchants have said they plan to offer free shipping with delivery by Christmas Eve for orders placed that day. Last year Free Shipping Day was on Friday, Dec. 16, and online sales totaled $1.072 billion, making it the sixth heaviest web shopping day of the 2011 season, according to web measurement firm comScore Inc.