Many Americans push off holiday shopping until the last minute, but there’s a catch with online shopping: Waiting too long may mean those gifts won’t arrive until after the holidays.

With consumers increasingly shifting their spending online, some retailers are lowering their free shipping minimums this year in a bid to lure more consumers to their online stores. However, the free shipping is typically available only to customers who order at least a week to 10 days in advance of Christmas.

Amazon (AMZN), for instance, has lowered its minimum free shipping threshold to $25, compared with $49 last year, but shoppers need to place their orders before Dec. 15 (see list below for additional store ordering deadlines), according to Phillip Dengler of BestBlackFriday.com.

As part of online retailers’ push to grab a bigger share of consumers’ holiday budgets, many now participate in Free Shipping Day, which will take place on Dec. 15 this year. About 1,000 retailers are participating, including JCPenney (JCP) and Target (TGT), although more will likely join in the next few days, said Sara Skirboll, shopping and trends expert at RetailMeNot.

Free Shipping Day “is a day when several online retailers offer free shipping with the guarantee they’ll deliver it to you before Christmas, Skirboll said. “One important thing consumers should know is that not every retailer participates in Free Shipping Day. Don’t assume that all websites will offer free shipping, and do some research before making your purchases.”

For shoppers who aren’t buying their gifts on Free Shipping Day, Skirboll recommends checking the shipping deadlines for retailers and making note of when packages are expected to arrive. It’s also worth checking whether another retailer might carry the same product but offer better guarantees on shipping, she added.

“Pay attention to the fine print,” she said. “Make sure you keep in mind how long the shipping takes but also the processing time as well. Sometimes orders might not get processed for a few days leading to some backup and delayed orders.”

It’s also possible to encounter delays at the shipping companies, such as UPS or the US Postal Service. UPS (UPS) already experienced some delays this holiday season, thanks to a higher-than-expected flood of online shopping after Thanksgiving.

Skirboll added, “It seems obvious, but the sooner you can get your shopping done the better. This gives you a buffer against any weather-related shipping delays or other reasons for your gifts not making it in time.”

Lastly, shopping online after Dec. 20 will likely lead to “exponential” costs for expedited shipping, she said.

Below are the deadlines for shipping at Amazon, Walmart (WMT) and other retailers, according to BestBlackFriday.com.

Amazon: Dec. 15 – Free shipping ($25 min.)

  • Dec. 18 – Standard shipping
  • Dec. 22 – Two-day shipping (free with Prime)
  • Dec. 23 – one-day shipping (In select cities)
  • Dec. 24, 9:30 a.m. local time or earlier – Same-day delivery (select cities)
  • Dec. 24, 9:45 p.m. local time or earlier – Two-hour delivery (select cities)

Bloomingdale’s

  • Dec. 20 by 5 p.m. ET – Standard
  • Dec. 22 by 12 p.m. ET – Express delivery

Kmart

  • Dec. 17 by 11:59 p.m. CST – Free shipping
  • Dec. 19 by 4 p.m. CST – Standard shipping
  • Dec. 21 by 4 p.m. CST – Premium shipping
  • Dec. 24 for in-store pickup

Kohl’s

  • Dec. 18 by 11 p.m. (CST) – Standard
  • Dec. 19 by 1 p.m. (CST) – Two-day shipping
  • Dec.  20 by 1 p.m. (CST) – One-day shipping

Macy’s

  • Dec. 20 by 5 p.m. ET –  Free standard shipping (min. $99)
  • Dec. 20 by 5 p.m. ET – Premium
  • Dec. 21 by 12 p.m. ET – Express
  • Dec. 24 by 10 a.m. ET – In-store pickup
  • Dec. 24 by 10 a.m. ET – Same-day delivery

Nordstrom

  • Dec. 20 by 12 p.m. ET – Two-business day shipping
  • Dec. 21 by 12 p.m. ET – Free standard shipping
  • Dec. 22 by 12 p.m. ET – Saturday delivery ($10)

Sears

  • Dec. 17 by 11:59 p.m. CST – Free shipping
  • Dec. 19 by 4 p.m. CST – Standard shipping
  • Dec. 21 by 4 p.m. CST – Premium shipping
  • Dec. 24 for in-store pickup

Target

  • Varies by item – Free standard shipping
  • Dec. 19 by 12 p.m. – Premium two-day shipping
  • Dec. 22 by 12 p.m. – Express one-day shipping
  • Dec. 22 by 7 p.m. – Restock

Toys R Us

  • Dec. 18 by 11:59 p.m. ET – Free shipping
  • Dec. 20 by 3 p.m. ET – Expedited
  • Dec. 20 by 11:59 p.m. ET – Express
  • Dec. 24 by noon ET – In-store pickup

Walmart

  • Dec. 13 – Freight
  • Dec. 19 – Standard
  • Dec. 21 – Rush

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