You’ve definitely heard of Amazon Prime Day even if you’ve never bought something during the event. It’s nearly impossible to avoid: leading up to the Prime member-exclusive sale, there’s commercials about it on YouTube, influencers posting about it on social media, flashy billboards advertising it in Times Square and media outlets (like NBC Select) telling you everything you need to know about it. At this point, Prime Day is fully embedded in consumer culture — that’s especially impressive considering it’s only been around for about a decade, and it’s not tied to the holiday shopping season like Black Friday and Cyber Monday are.Ever since its inception, Amazon has scaled Prime Day to record-breaking heights. The event generates billions of dollars in global sales and drives up e-commerce activity across retailers. This year, Prime Day is expected to make history as Amazon’s most profitable sale ever, even though the retailer is making major changes to its format: It’s one month earlier than usual and four days long rather than the typical two.To contextualize Prime Day and its impact on e-commerce before this summer’s sale (which is happening from Jun. 23 to 26), I charted its history over the past 11 years. I also consulted experts about its growth, what it signals about consumer behavior and whether deals really are some of the best ones you’ll see all year.Want more from NBC Select? Sign up for our newsletter, The Selection, and shop smarter.How did Prime Day start?The first-ever Prime Day took place on July 15, 2015 to celebrate the company’s 20th anniversary, according to Amazon. It lasted 24 hours and was available to members in nine countries. Since 2015, Prime Day has expanded its reach — Amazon now hosts the sale for four days in over 20 countries, and it runs a second version of Prime Day, Prime Big Deal Days, in October to kick off the holiday shopping season.One of the factors that makes Prime Day so unique is that it’s an event Amazon manufactured, unlike Black Friday and Cyber Monday, both of which are tied to the holiday shopping season. Prime Day (the first one, anyway) is traditionally held between the end of June and mid-July, which is a strategic decision on the company’s part: The summer is a slow period for retailers, and Prime Day is an attempt to remedy that. “Prime Day provides Amazon with a jolt during an otherwise dormant shopping season,” says Dr. Ross Steinman, a professor of consumer psychology at Widener University. Hosting Prime Day during the week is a strategic decision, too: Summer weekends are reserved for relaxing, sleeping in, leisure activities and traveling, but Amazon knows it can capture shoppers’ attention during the week when they’re using their phones and computers more.Why does Amazon host Prime Day?There’s three big reasons why Amazon hosts Prime Day: to attract new Prime members, retain the members it already has and drive sales to its marketplace. Amazon’s goal is to accrue an army of repeat shoppers who take advantage of everything a Prime membership offers them year-round, not just during one big sale. Prime Day acts as an entry point for new Prime membership sign-ups, and a way to remind existing members why the loyalty program is worth $139 a year. The sale puts Prime’s benefits on full display and exposes shoppers to the retailer’s “ecosystem of consumption,” meaning its network of platforms like Prime Music, Whole Foods grocery delivery, Prime Video, Audible and Kindle Unlimited. And once you’re in Amazon’s ecosystem, it’s hard to leave, says Steinman. “Amazon’s goal is to be sticky,” he says. “Consumers in the Amazon ecosystem are going to spend largely double what non-Prime members will.”As for driving sales to Amazon’s marketplace, hundreds of brands offer deals during Prime Day, but those the retailer owns, like Fire, Kindle, Ring and Blink, tend to drop prices the most. Discounting Amazon-owned devices is particularly lucrative for the retailer because they’re designed to increase your purchases on Amazon, says Steinman. The majority of this tech is equipped with Amazon Alexa, a virtual assistant who can notify you about deals and make purchases if you give her permission.There’s one more reason Prime Day is such an important event for the company: “It’s a stress test for the holidays,” says Steinman. “Prime Day creates an artificial surge in orders, similar to what the retailer experiences between November and December, so it provides Amazon with an opportunity to do a test run. They can see if they need to work out any kinks as they get closer to the formal holiday shopping season.”How long is Amazon Prime Day?Amazon Prime Day started as a 24-hour event in 2015, and it gradually extended in length before becoming known as a 48-hour event between 2019 and 2024. Then, in 2025, Amazon doubled Prime Day to four days, which seems to be the new norm, at least for now — 2026 is the second year with this timeframe.Experts agree that making Prime Day four days long was a wise move on the retailer’s part, but there’s more to it than assuming more time to shop equals more purchases — it’s also about optics. “When you expand into a four-day event, you’re really putting an anchor down and saying, ‘this is a Black Friday shopping type moment,’ signaling to consumers that’s what they should expect,” says Vivek Pandya, the manager of Adobe Digital Insights. Extending Prime Day aligns with shoppers’ general awareness around the sale, too. Hosting it under a tight time constraint built hype, which worked well to draw consumers in during the early years. But now, Prime Day is permanently embedded in the retail calendar, so Amazon doesn’t need to build the same type of excitement around it. Instead, the retailer may as well give shoppers the opportunity to make multiple transactions, says Pandya.Finally, a four-day sale acknowledges that consumers are adopting more advanced budget management strategies as they’re concerned about the current volatile economic environment, says Steinman. They’re deliberately looking for deals using browser extensions to track prices, for example, because they want to find real value — a longer timeframe to shop lets them do so.What were the results of Prime Day 2025?Experts were certain that Prime Day 2025 would see major growth since it was four days long for the first time ever. The results, however, blew their predictions out of the water. Amazon doesn’t disclose sales figures, but Adobe estimates that U.S. retailers drove $24.1 billion in online spending from Jul. 8 to Jul. 11, the period during which Prime Day took place — this represents 30.3 percent growth year-over-year, and is more than two of 2024’s Black Fridays. These figures cement Prime Day’s identity as the summer sale, and they show how much other retailers have embraced hosting corresponding, competing savings events. It’s undeniable that Amazon has achieved its goal of making shopping activity flourish during an otherwise sleepy retail season.Prime Day 2025 bestsellersBestselling items from Prime Day 2025 include Premier Protein Shakes, Dawn Platinum Powerwash, Liquid IV packets and Amazon Basics paper plates, according to Numerator. These items are all personal purchases you need to frequently restock, which tells experts that people are mostly shopping for themselves during Prime Day. The event is during the summer, so members buy items they need, unlike Black Friday and Cyber Monday, which people use to buy items they want, as well as holiday gifts.What to expect from Prime Day 2026Over a decade in, shoppers thought they knew what to expect from Prime Day. But for the second year in a row, Amazon threw them a curveball: It’s hosting the 2026 sale in June rather than July, and repeating the four-day format.Scheduling Prime Day for June isn’t unheard of — Amazon did it once before in 2021. But after years of building a habit among Prime members and teaching them to plan for major deals in July, it could be a risky move, says Melissa Murphy, an adjunct professor at Carnegie Mellon University’s Tepper School of Business. So why did the retailer do it?I spoke to Jamil Ghani, the vice president of Worldwide Amazon Prime, who says Amazon thinks deliberately about the ideal timing for its mega sale every year. Given Father’s Day, the United States’ 250th anniversary on July Fourth and the World Cup coming up in the next few weeks, hosting the sale beforehand makes sense — the June date lets shoppers prepare for each event by saving on related products. Ghani says Amazon got positive feedback from its loyalty members about 2025’s four-day timeframe, so the retailer kept it for 2026. Shoppers liked the additional time to discover new brands, find the best deals from their favorites, curate their shopping cart and check out when they were ready, rather than in a rush.Even with the date change, Pandya expects to see high year-over-year growth for Prime Day 2026 (Adobe hasn’t released official estimates yet). It won’t be nearly as much growth as last year since Amazon isn’t making the sale longer (again), but it will likely be significant — and as counterintuitive as it sounds, that’s in part due to consumers’ economic concerns around inflation and the rising cost of living. “During most of the year, consumers are pulling back on non-essential spending to manage high costs, but once retailers present them with deals that they see strong value in, they’ve been over-indexing on spending,” says Pandya.One final thing experts are monitoring going into Prime Day 2026: how moving the sale to June impacts total e-commerce sales in July. The event drives up online shopping activity across the board and massively contributes to sales for the month it happens in. Pandya says June 2026 could end up pulling numbers that result in year-over-year growth we haven’t seen since the Covid-19 pandemic solely due to Prime Day’s schedule change. That would likely leave a huge gap in July that other shopping-heavy events couldn’t fill.What are the best products to buy during Prime Day?There’s an inaccurate stereotype about shoppers during huge sale events like Prime Day, says Steinman. “The perception is that somebody’s going to get swept up in excitement and engage in a number of impulse purchases,” he says. “But by and large, that’s not what happens on Prime Day.”For the most part, Prime Day shoppers are savvy — they’re conscious about using the sale to their advantage and spending strategically, says Steinman. Many compare prices across retailers to determine whether a deal is worth taking advantage of, and save their “bucket list” purchases for Black Friday. That’s not to say Prime Day shoppers ignore deals on luxury or “non-essential” items. There’s almost always an uptick in spending on cosmetics, apparel and tech during the event, which is balanced with spending on household basics and groceries, says Pandya.Shoppers don’t know exactly what Amazon is discounting on Prime Day until the sale starts, which is part of the event’s allure. Prime Day bestsellers vary from year to year and from country to country, which isn’t just the result of different buying habits — deals in one country aren’t always reflective of another. But factors, like a discount being well-advertised or well-priced, can contribute to a product becoming a bestseller, as can Amazon’s agenda of selling as many of its devices as possible. Brands also use Prime Day to slash prices on soon-to-be out-of-season or out-of-style merchandise.Some of the best Prime Day discounts are Amazon’s Lightning Deals, flash sales that give shoppers a short window to purchase limited quantities of specific products. Lightning Deals put shoppers in a competitive mindset and add what Steinman calls a “gamification” aspect to the sale. Shoppers don’t have time to think about whether they need the item being sold as a Lightning Deal, so they impulsively buy it because they don’t want to miss out.How does Prime Day impact other retailers?By hosting Prime Day between the end of June and mid-July, Amazon permanently altered the retail calendar. It created the blueprint for a member-exclusive flagship summer sale, and proved that it’s powerful enough to create a halo effect on e-commerce by driving purchases to other sites as well as its own. That forced competitors like Walmart, Target, Macy’s and Best Buy to respond.Since the first Prime Day in 2015, many retailers have changed the timing of their biggest sales to align with Amazon’s, or created new ones, like the Walmart Deals event and Target Circle Deal Days. Amazon’s competitors hope that shoppers will spill over onto their sites and make additional purchases, which happens often. In 2025, 35 percent of Prime Day shoppers either shopped or planned to shop Target Circle Week, 49 percent shopped the Walmart Deals event and 11 percent shopped Best Buy’s Black Friday in July, according to Numerator.“Amazon is in the driver’s seat, but retailers acknowledge that this is a real opportunity for them to capitalize on, so they need to employ all forces to help enable spending,” says Pandya.Because Amazon moved Prime Day up to June this year, Murphy expects other retailers to do the same with their 2026 summer sales. So far, Target has — it’s hosting Target Circle Deal Days from Jun. 23 to 26, perfectly overlapping with Amazon’s event. “Any really strong retailer is going to be a fast follower of what Amazon is doing and when, and piggyback onto the timing of its event,” says Murphy. “They’ll try to leverage that opportunity.” If any retailers opt to keep their summer sales in July, Pandya says it may be because they don’t want to risk having a softer July, even if that means they won’t get Prime Day spill-over shoppers.What is Prime Big Deal Days?For the first time in 2022, Amazon hosted two Prime Day-level events in one year: Prime Day in July and the Prime Early Access Sale in October. Amazon has followed that schedule ever since, but changed the name of the fall event to Prime Big Deal Days. (The retailer has not confirmed Prime Big Deal Days 2026 yet, but we expect it to happen this October.) Shoppers originally didn’t see much of a difference between Prime Big Deal Days and Prime Day, but the retailer made them more distinct in 2025: It expanded the summer sale to be four-days and kept the fall sale to be 48 hours, creating a hierarchy where the longer sale is perceived as “better” than the shorter one.Although hosting a second Prime Day-level event in the fall takes away some of the novelty the summer sale became known for, it’s Amazon’s attempt to kick off the holiday shopping season. Many of the retailer’s competitors now start their early Black Friday promotions in October to give shoppers extra time to buy gifts, a trend Steinman calls “seasonal shopping elongation.” Amazon wants to participate in this trend, so it added the October sale while still trying to recruit more Prime members, says Steinman. “It plays on shoppers’ fear of missing out on a great deal by creating the idea that member-exclusive events can take place at any point,” he says.Amazon doesn’t disclose sales figures, so we don’t know exactly how Prime Big Deal Days compares to Prime Day in terms of revenue. Typically, however, discounts during the October event are lackluster compared to July, and people don’t feel the same level of pressure to shop, experts say. The summer isn’t filled with opportunities to take advantage of sales beyond Prime Day, which works in its favor. But shoppers know that Black Friday and Cyber Monday deals start as early as October across dozens of retailers, so they usually don’t approach Amazon’s fall savings event with urgency.Meet our expertsAt NBC Select, we work with experts who have specialized knowledge and authority based on relevant training and/or experience. We also ensure that all expert advice and recommendations are made independently and with no undisclosed financial conflicts of interest.Dr. Ross Steinman is a professor of consumer psychology at Widener University.Vivek Pandya is the manager of Adobe Digital Insights.Melissa Murphy is an adjunct professor at Carnegie Mellon University’s Tepper School of Business.Jamil Ghani is the vice president of Worldwide Amazon Prime.Why trust NBC Select?I’m a reporter at NBC Select who has covered Amazon since 2020. I write about the retailer’s biggest sales (Big Spring Sale, Prime Day and Prime Big Deal Days) and frequently update NBC Select’s Prime membership guide. I also regularly appear in related NBC News NOW and TODAY segments. For this article, I researched the history of Prime Day and spoke to three experts. I shared trends I’ve noticed first-hand over the years, too.Catch up on NBC Select’s in-depth coverage of tech and tools, wellness and more, and follow us on Facebook, Instagram, Twitter and TikTok to stay up to date.