The holiday shopping season began early this year, with 41 percent of Americans starting their shopping in October or earlier. A shopper takes part in the annual Pajamarama event in Takoma Park, Md., in early December. (Sarah L. Voisin/The Washington Post)

There’s Black Friday, Cyber Monday and Small Business Sunday. Now another frenzied affair joins the shopping lineup: Holiday Hangover Day.

In 2017, it falls on Tuesday, Jan. 3, the day most Americans head back to the office.

According to sale-tracking website Brad’s Deals, retailers see a discernible uptick in online sales on that day, as Americans log in from their cubicles to buy jewelry (often for themselves), fitness equipment (to fulfill those pesky New Year’s resolutions) and bedding and linens (which promise a fresh start to the year). In 2016, there was a 15 percent spike in online sales on Monday, Jan. 4, compared with surrounding days. The year before, it was 10 percent.

“Shoppers are getting back into their daily routines. They’re back in the office, sitting in front of a computer again, with a list of things Santa didn’t bring and a stack of gift cards they have to spend,”  said Rebecca Lehmann, a spokeswoman for the site, which coined the phrase “holiday hangover day.” “It’s a perfect storm that adds up to a bigger-than-usual shopping day.”

This holiday season has been a good one for retailers. Overall sales are expected to be 4.9 percent higher than last year — marking the largest jump in sales growth since 2005, according to Customer Growth Partners, a research firm in New Canaan, Conn. Online sales, meanwhile, are on track to grow 15 percent.

Americans “are shopping at a rate not seen since the mid-2000s,” Craig Johnson, president of Customer Growth Partners, told the Wall Street Journal this week.

Now retailers are hoping to keep some of that momentum going.

A few days after Christmas, the daily deals site Zulily was advertising “Everything you need for Christmas next year,” while J. Crew Factory sent out emails that said, “PSA: It’s OK to shop for yourself again.”

It’s no secret that retailers have long relied on after-Christmas sales to help clear excess inventory and rack up sales. This year, 48 percent of Americans — and 80 percent of millennials — said they plan to shop in after-holiday sales, according to a survey by the National Retail Federation.

“The new year brings shoppers into stores for many items, especially fitness,” a spokesman for Sears said in an email, adding that the company will kick off its semiannual “blowout sale” on Jan. 1, with deals on fitness equipment, jewelry and home appliances.

The holiday shopping season began earlier than ever this year, with more than 40 percent of Americans saying they had bought their first present by October, according to a survey by the National Retail Federation. The biggest shopping day so far: Dec. 17, when an estimated 156 million Americans turned up to spend.

And increasingly, consumers say they’re looking to buy for themselves, too — particularly after the holidays. Americans are expected to spend an average of $139.61 on themselves this season, up from last year’s $133.74, according to the survey.

“Many shoppers are taking the approach of ‘one for you, two for me’ this holiday season,” said Matthew Shay, chief executive of the National Retail Federation. “Retailers are preparing by offering a wide array of merchandise and promotions — items shoppers want to give as great gifts at prices so good they want to buy for themselves too.”

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