Amazon completely invented Prime Day, and now it has grown to rival Black Friday and Cyber Monday

AP/Lynne Sladky

Prime Day is coming, and so are a whole lot of Amazon packages to customers' doorsteps.

• Amazon Prime Day is right around the corner, and so is one of e-commerce's biggest days of the year.
• The day has grown in both length of time and sales over the years, as have the breadth and depth of the deals.
• Many of Prime Day's deals are actually better than those that happen with other sales holidays during the year, like Black Friday.
• Other retailers are now announcing deal days of their own to coincide with Prime Day.
• Prime Day is growing quickly, and it could someday be one of the biggest days on the entire retail calendar.
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Amazon Prime Day is coming, and the wave it is riding is higher than ever before.

The event has grown to become one of the biggest of the year in e-commerce. It's also on the fast track to becoming a force to be reckoned with in all of retail.

Starting with the obvious, Amazon has stretched the day itself to encompass two full days.

But the deals themselves are also going to be better than last year, according to experts.

In fact, 70% of the deals Amazon will offer on Prime Day will be better than Black Friday 2018, according to a prediction by Offers.com and BestBlackFriday.com. Last year, 67% of Prime Day prices were better than the previous Black Friday.

Read more: Amazon is ensuring everybody can cash in on this year's Prime Day deals, and it's a sneaky strategy to boost its most important asset

Sales are growing, too. Amazon is predicted to move a mammoth $5.8 billion worth of goods globally just on Prime Day, according to Coresight Research. That compares to the estimated $3.9 billion it moved in 2018.

Around 76% US Prime members told Profitero in an survey they plan to shop on Prime Day, compared to the 63% who shopped last year. Of those shoppers, 56% said they expect to spend more in 2019 than they did last year.

But with all that excitement, it's clear Prime Day has gotten so big that it is no longer limited to just one retailer - even the retailer that invented it.

"What we are seeing is that Prime Day isn't just an Amazon holiday anymore," Taylor Schreiner, principal analyst at Adobe Digital Insights, said in a prepared statement. "Retailers have had a competitive response to the event over the past few years. In fact, research shows that more than 250 retailers are gearing up to convert Prime Day traffic this time around."

It seems every retailer is now jumping in to capture the "halo effect" of deals on this Black Friday in July. Walmart, which has "Google week," and Target, which has "deal days," are the biggest retailers that have announced deal events, but so has Best Buy with its "big deal days" and eBay with its tongue-in-cheek "crash sale," referencing the fact that Amazon.com crashed and was down for nearly an hour during last year's Prime Day.

Smaller retailers and direct-to-consumer shops have announced their own promotions, too.

There's a reason for these retailers to do so, as that halo effect is becoming increasingly pronounced. Retailers that aren't Amazon will see a 79% lift in sales during Prime Day, Adobe Analytics predicts. Last year, that figure was only 60%.

Retailers with a large store footprint may also be able to steal some sales away from pure-play e-commerce joints as customers increasingly prefer to use the buy-online-pickup-in-store option during large sales periods, Adobe Analytics said.

It's clear that Prime Day has officially secured its place among the pantheon of retail's high holy days.