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How Amazon is preparing for its annual megasale on Prime Day, its reign as the country’s largest online retailer is impressive: it is expected to generate more than 40% of the country’s e-commerce sales by the end of 2021.

Amazon’s dominance on the internet has only grown as online shopping becomes second nature for many consumers. This is exactly what has happened in the past 13 years.

In 2008, e-commerce sales represented only 3.6% of total retail sales in the United States, according to eMarketer. After growing gradually year on year, that number rose to 14% in 2020 as the Covid pandemic boosted online spending on everything from groceries and toilet paper to spinning wheels and workout clothes. Ecommerce sales are set to account for 15.3% of total retail sales by the end of this year and grow to 23.5% by 2025, eMarketer said.

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In second place behind Amazon and well behind the big box chain Walmart is expected to occupy about 7% of the digital retail market this year. Follows the two Ebay, Apple, Home depot, aim and Best buy, according to eMarketer.

As in previous years, Walmart and Target are holding competing deals events that coincide with Amazon Prime Day 2021. Both discount stores will start selling on Sunday, but Walmart’s offerings will extend through Wednesday, while Target and Amazon will end on Tuesday. Both Walmart and Target are hoping to reach customers who are already browsing the web for summer discounts on Prime Day.

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According to a recent research report of JPMorgan, Amazon is well on its way to overtaking Walmart as the largest US retailer in 2022 as it gains a growing share of the overall e-commerce market. The accelerated adoption of internet shopping by consumers during the Covid pandemic has also given other Amazon businesses a boost, JPMorgan said.

EMarketer predicts that total US digital revenue on Prime Day will grow 17.3% year over year to $ 12.18 billion. Sales, which will be exclusively on Amazon on Prime Day, will increase 18.3% from 2020 levels to $ 7.31 billion, it said.

Reporting on Amazon Prime Day 2021

Read more about Amazon and others scheduled for this year’s sales events:

Last year Amazon’s typical July time for its shopping extravaganza was postponed until October due to the pandemic. Prime Day finally marked the unofficial start of the Christmas shopping season.

Back to a more normal schedule, this year’s event has been postponed a bit in June. Experts say the company wants to increase spending in what is typically a slower time on the retail calendar. The new time could also lead to an earlier start shot for back-to-school shopping.

“Amazon will be shy when they announce this … so they have the benefit of knowing what they are doing to make sure they are in a good position,” said Rod Sides, vice chairman of retail and sales at Deloitte said in an interview. “While the others answer.”

—CNBCs Nate Rattner contributed to this report.