Ties. Dozens of patterns, colors and fabrics — discounts on 300 different styles. That’s what Nordstrom had planned for its big sale last July. The company had worked with trend forecasters and talked with designers, but history was its best guide. Based on previous sales, the retailer was confident that shoppers would be seeking out deals on office wear like ties, dresses, heels and handbags. By the end of February, it had ordered everything it planned to sell at the event.

Months later, the world had rearranged itself in a way no trend forecasters could have predicted. The summer sale was pushed to August and had just 15 types of ties. (People did still sometimes dress up for Zoom calls.)

“There was nothing for staying home and working remote,” Teri Bariquit, Nordstrom’s chief merchandising officer, said in an interview. The retailer threw itself into tracking terms that newly isolated customers were searching for on its website and on Google (“cozy” and “slippers” among them). It frantically contacted suppliers to buy more activewear and children’s apparel. And it created a tool so that customers could build lists of products they wanted from the sale before it even started.

The world of retail runs on predicting the future. What you buy in July was decided on in November. Trendspotting used to happen largely in person — retailers had eyes and ears on the ground, hunting for cool. Now it is an obsessive study in web traffic and reviews, Instagram and TikTok posts, bridal registry data and restaurant and hotel bookings. This was always a piece of the puzzle for many chains, but it became central to their survival in the past year.

So as we are preparing to head back into the real world, what we will wear and buy once we’re out there is being dictated more than ever by our lives online.

Big retailers have been feeling enormous pressure to make the right bets on what consumers will want in the second half of 2021 and beyond. Apparel sales in the U.S. declined 19 percent overall last year, while fashion footwear sales declined 27 percent, according to the NPD Group. A long list of pandemic bankruptcies included Brooks Brothers and the owner of Ann Taylor and Loft, while many other large chains laid off workers and closed stores.

Madewell, which is owned by J. Crew Group, has long relied on a panel of about 5,000 brand enthusiasts to weigh in on new products and styles. But once the pandemic hit, the company suddenly needed less on hemline lengths and more on what exactly their customers were doing every day. It was a shift in focus that many retailers made, and it seems likely to last well beyond when stores fully reopen around the world.

“Trends become irrelevant, and it really became about how people were living and what they were doing and how they were feeling,” Anne Crisafulli, Madewell’s senior vice president of merchandising said. “Those are the questions we started asking. It was less about, ‘Are mini dresses in or out,’ or ‘What prints are in?’”

What we wore in 2020

A festive cape, draped from your shoulders, paired with a dress and glitzy heels while you sip on mulled wine. That’s the sort of scene Macy’s was envisioning for holiday parties in 2020, before the reality of Zoom nights in living rooms.

“We really felt good about this dress-up opportunity, people really feeling glam,” said Nata Dvir, Macy’s chief merchandising officer. “We were thinking about outerwear being as bold as capes.”

Bloomingdale’s, which is owned by Macy’s, had forecast “a mix of utility and romanticism,” which would have included puff sleeves, eyelets and maxi dresses, said Denise Magid, an executive vice president at Bloomingdale’s who oversees ready-to-wear apparel.

Major department stores have fashion offices filled with undisclosed numbers of employees who keeping track of new styles, surfing social media and liaising with designers. Big retailers also usually subscribe to online services that aggregate signals from Google Trends and social media. They work with agencies that specialize in fashion forecasting, like Stylus and WGSN, which project broader consumer habits along with more granular details like seasonal color palettes, textiles and silhouettes. They all also obsessively track their competition.

Much of that work used to take place in person. WGSN, for example, offered city guides to American retail buyers on trips abroad. “If a buyer from a department store wanted to go to Paris, we’d have a guide that would tell them where to go and eat and which stores they should see for different things,” said Francesca Muston, the vice president of fashion content at WGSN. Runway shows were also important. At Bloomingdale’s, before the pandemic, “runway was a huge component of what we were forecasting, because what you saw on runway would trickle down to other collections,” Ms. Magid said.

As everything went virtual last year, including runway shows, social media took on new importance, and retailers rushed into anything that smelled like a trend, sometimes tapping Los Angeles-based manufacturers to help them out on a faster timeline.

“Instagram and TikTok have filled that void, and it kind of changes the dynamics again about speed and being reactive because things have a shorter life span,” Ms. Magid said. She recalled an overnight surge in demand for denim joggers in the fourth quarter after a “famous influencer” (the retailer wouldn’t say who) wore a pair by Rag & Bone on an Instagram Story.

“We happened to have it,” she said. But then the question became, “‘How quickly can we get more joggers on the floor?’ And it was in a matter of weeks we were able to react.”

The industry has undeniably been battered in the past year. But there were some bright spots, and retailers were able to make certain shifts, including last minute buys of slippers and lounging garb before the holidays.

TikTok also fueled a cottagecore trend, as characterized by long billowy dresses, “which has been huge for our clients,” said Ms. Muston. “It spoke to a need for escapism and fantasy at a time when people were locked up,” she said. When people did go outside, to eat under a restaurant heat lamp or to take a walk as their primary leisure activity, cottagecore was perfect, Ms. Muston said. It “spoke to that whole reconnection with nature.”

What we’ll be wearing for the rest of 2021

Jenn Hyman, Rent the Runway’s chief executive, knows what she doesn’t want to see anymore. As she told the clothing rental company’s buying team in September: “If it was lounge-y enough, comfortable enough, boring enough, gray enough to wear in 2020, we’re not buying it for 2021.”

Rent the Runway, which is popular for special occasions and workwear, plans much of its business three to six months in advance. To try and predict an unpredictable future this year, the company said it had been studying traffic on streets, OpenTable and airline bookings, and office occupancy rates in big cities to understand the economic recovery and demand for its goods.

“We got to the point where we were calling wedding venues in top destinations around the country to understand what their bookings were,” Ms. Hyman said.

The site has also reaped data from customers reserving specific dresses and other items ahead of time and adding “hearts” to desired items. It can see when women build collections of potential rental clothing with labels indicating whether they’re for birthdays, honeymoons or other events.

“We started seeing very interesting, very different data, starting at the beginning of February, that led us to believe that the recovery was going to happen earlier and at a steeper clip than what we originally had forecast,” Ms. Hyman said.

Bloomingdale’s has been watching people add new wedding dates to its bridal registries and has gleaned insights from its Florida stores, which opened earlier than elsewhere in the country. People came in “wanting sexier dresses, bodycon dresses and going out tops,” Ms. Magid said, which could be an early indicator for the rest of the country.

That demand prompted the retailer to seek dressier options than the “very casual” styles that vendors were showing the chain between the fall and March, though it noted that comfort remained key. She said that some of the whimsy and romanticism that the retailer had expected in 2020 could appear later this year as part of a possible “prairie trend.” (Indeed, the puff sleeve has become perhaps too ubiquitous in recent weeks.)

Macy’s saw consumers search for prom dresses in December even though they weren’t ready to purchase them, which gave the retailer confidence that proms, canceled last year, would actually be a thing in 2021. “People tend to browse before they’re really ready to convert,” Ms. Dvir of Macy’s said. “We had anticipated that it would be good because we did see people were searching as early as they had been. Same with wedding, mother-of-the-bride dresses.

Despite the shock of the pandemic, retailers are cautiously optimistic about the year ahead — a sentiment buoyed by retail sales in March, which beat expectations and rose by nearly 11 percent, including a 23 percent jump in clothing and accessories. Sales have since fluctuated, keeping their optimism in check.

There is even good news in a potential mass movement to high-waisted, loosefitting, generation-dividing jeans away from a decade of skinny denim dominance. It offers hope that consumers are ready for something new.

How we’ll know what to wear from now on

Comfort does still reign king. Many retailers are hedging their bets, describing the importance of being “nimble” with inventory and championing “versatility” in their apparel assortments in 2021. There is a big focus on clothes that are designed to be worn between home and hybrid work and to post-hybrid work cocktails.

“I’m not super stressed if people are going to have weddings and things like that,” Ms. Crisafulli of Madewell said. “We’ll add and buy into dresses if that really starts to pick up, but where we’ve been more focused is this shift back into real life and what day-to-day life is going to look like.”

Ms. Muston of WGSN said her firm’s forecasts “have been looking much more at adaptability and versatility in something like dresses.” That extends to ideas like tying them in different ways for unique looks or crafting removable collars to maximize single garments. Versatility also connects to key ideas around conscious consumption and sustainability, which will also probably guide at least some portion of shoppers in the next year.

Retailers have been trying to find ways to shorten their time horizons — for department stores, private labels like Aqua at Bloomingdale’s often offer the best vehicle for jumping on whatever is striking it big on TikTok or Instagram. Madewell said that it can make shifts to its clothing in as little as eight weeks and that it has been testing demand for some items on its website before fully releasing them.

Nordstrom merchants, who initially predicted that shoppers would flock to its workwear and office dresses in the summer of 2020, have been talking with designers about how those definitions are changing as it prepares for this year’s sale, which is scheduled for the end of July. This time, even as stores are open, the company is bringing back the ability for customers to make digital wish lists of sale items before the event starts and said it is offering ways for shoppers to digitally communicate with salespeople.

“No one is envisioning a customer wanting to come back in with four-inch stilettos and a buttoned-up suit and tie,” Ms. Bariquit said. She is confident people will want to get dressed up again, she said, but thinks they will dress for work in a different way.

Customers are telling the retailer that they “love the comfort they’re feeling in their joggers, yet they don’t want to wear their joggers to the office,” she said. “So how does that translate to soft pants of the future?”