Amazon is permanently changing Americans' holiday shopping calendar by celebrating Black Friday-style sales in July.
The ecommerce giant is holding its third annual Prime Day on Tuesday, and it's expected to be bigger than ever before.
Amazon started the sale several hours earlier this year, compared to the last two years, and more than a dozen other major retailers are now taking part by offering their own massive sales events to counter Amazon.
RELATED: Check out the best Prime Day deals under $100:
Toys R Us, for example, is having its biggest sitewide sale of the year now through Wednesday, and Macy's is offering 60% off its entire website on Monday and Tuesday.
JCPenney meanwhile is holding a "Penney Palooza" sale, offering 25% its entire website and additional discounts on certain items.
Home Depot, Lowe's, and Best Buy are also offering 40% off deals on appliances until Wednesday.
In addition to running their own promotions, many retailers are promising to price-match Amazon's Prime Day deals. These retailers include Jet.com, Best Buy, Toys R Us, Babies R Us, Target, Sears, Home Depot, and Bed Bath and Beyond.
Prime Day is only in its third year, and it's still a long way from catching up to Black Friday in terms of total sales.
The sales event has been estimated to generate about a half billion dollars for Amazon, while on Black Friday last year, ecommerce sales totalled $3.34 billion, according to Adobe.
RELATED: Check out the best Prime Day deals under $50:
But the deals are better than what shoppers might find on Black Friday, according to BestBlackFriday.com.
The website analyzed Amazon's deals on Black Friday and Prime Day and found that in 2016, 77% of Prime Day prices were better than comparable deals offered on Black Friday.
As Prime Day grows in popularity, shoppers' interest in Black Friday has been waning.
Last year, about 154 million customers shopped in store and online over the Thanksgiving holiday weekend, down from 226 million in 2011, according to the National Retail Federation.
More from Business Insider:
Amazon is struggling with on-time delivery in Japan
How to get free Chick-fil-A next week
The vast majority of Starbucks workers say in a new survey that the chain needs to fix a major problem