Christmas is fast approaching, but for those ordering gifts online, last call for Santa's sleigh is still days away.
Wednesday, Dec. 18 is Free Shipping Day, an event organized by coupon site FreeShipping.org as a kind of final shot for online shoppers to get free standard shipping with holiday delivery. More than 925 e-tailers are participating, including Harry & David, Neiman Marcus, Sports Authority and Eddie Bauer. "Some of the retailers, their end-all-be-all date for standard shipping is the 18th," said spokeswoman Kendal Perez.
But if there are more gifts left on your shopping list after Wednesday, there's no need to brace yourself for a mall trip. "You still have a lot of wiggle room," said Louis Ramirez, a senior writer for deal-tracking site DealNews.com. "If you find yourself on Monday or even Tuesday missing a gift, you don't necessarily have to rush to the store."
A shorter shopping season and growing online sales have pushed sites to extend shipping deadlines, said R.J. Hottovy, director of consumer equity research for Morningstar. "Retailers seem to be expecting a lot of last minute orders," he said. "We have seen the deadline get extended, up to the very last minute."
American Eagle, J. Crew, and Sears are among the retailers who have standard shipping deadlines on Dec. 21. Amazon announced this week that members of its $79-a-year Prime service can place orders as late as midnight on Dec. 22. Nordstrom's last-call for free standard shipping on some items is 3 p.m. EST on Monday, Dec. 23, while Zappos.com will take Christmas orders through 7 p.m. that day.
Even retailers with earlier cutoffs typically offer free or discounted expedited shipping as the holiday gets closer, said Ramirez. Neiman Marcus has a promotion on its home page offering free rush delivery through 1 p.m. EST on Dec. 21 with code NMRUSH.
For Christmas Eve shoppers in some cities, there's even same-day delivery on select items via Amazon.com, Google Shopping Express, eBay Now and others—although shoppers will still have to contend with early cutoffs (Amazon's is 7 a.m. in Chicago and Indianapolis) and, in some cases, delivery fees. In November, eBay Now announced it would waive its usual $5 fee through Christmas Eve, while Google Shopping Express is offering new users six months of free same-day deliveries.
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But even if the option is there, be cautious about waiting too long. Snowstorms and inventory shortages can prevent a last-minute order from being processed or delivered on time, Hottovy said. Case in point: In 2011, Best Buy announced four days before Christmas that it wasn't able to fill some online orders. "You have to be aware of that risk," he said. Check delivery date estimates before purchase.
—By CNBC's Kelli B. Grant. Follow her on Twitter .