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Amazon.com (NASDAQ:AMZN) stock is on fire lately. Shares of the online retailer are up by more than 50% year to date, and trading near historical highs in the neighborhood of $475 per share. Amazon is scheduled to report earnings on Thursday, July 23, and this could be a make-or-break moment for the company. Will the upcoming earnings report from Amazon provide more upside fuel or a reason to take profits?

It's all about sales growth
Amazon is a growth company, not only because the business is expanding rapidly, but also due to its strategy and capital allocation policy. It is aggressively investing in areas such as its logistics and distribution network, digital content, and cloud computing infrastructure, among others. These investments are hurting profit margins, and it's important for Amazon to continue growing at a strong rate so that top-line expansion provides justification for the company's razor-thin profit margins.

One of the main reasons why Amazon stock is doing so well lately is that revenue growth has been quite encouraging. Net sales during the first quarter of 2015 were $22.72 billion, a 15% increase year over year. Excluding the unfavorable impact from changes in foreign exchange rates, net sales grew by a vigorous 22% annually last quarter.

Wall Street analysts are on average expecting $22.37 billion in total revenue during the second quarter of 2015; this would represent a year over year increase of 15.7% from the same period in 2014. The company's guidance is for revenues to be in the range of $20.6 billion to $22.8 billion, or to grow between 7% and 18%. This means that analysts' forecasts are near the top end of Amazon's revenue guidance.

Why Amazon Prime is important
Amazon Prime is a crucial driver for Amazon, as Prime members are more loyal to the company and tend to spend more money on their purchases. Amazon does not disclose precise membership numbers, but the company has admitted that it has tens of millions of them.

According to a recent report from Consumer Intelligence Research Partners, Amazon could have as much as 44 million Prime members in the U.S. as of June 2015, gaining 3 million new members during the second quarter of the year. The research firm estimates that Prime members account for a big 47% of all Amazon customers, and that they spend on average $1,200 per year versus $700 per year for non-members.

On July 15, Amazon launched its first ever "Prime Day," a special anniversary sale offering exclusive lightning deals to Prime members. The company has reported that this was a big success from a commercial point of view, as global customers ordered 34.4 million items, breaking all Black Friday records with 398 items ordered per second. According to Amazon, more new members tried Prime worldwide than in any single day in the company's history.

Prime Day numbers will not be included in financial reports for the quarter which ended in June, and the company is quite secretive on this key program. But both analysts and investors will most probably pay a lot of attention to any kind of available information on Amazon Prime and its overall impact on the business.

Cash flow and earnings
Since Amazon remains in heavy reinvestment mode, earnings tend to be quite volatile from quarter to quarter and hard to predict. As a reference, management is expecting operating results in the second quarter to be between a $500 million loss and a $50 million operating gain.

Wall Street analysts estimate on average than Amazon will report a net loss of $0.14 per share, but there is a lot of dispersion in those forecasts. The most pessimistic estimation is for a net loss of $0.61 per share, while the most bullish one calls for a net gain of $0.38 per unit.

Operating cash flow is probably a more important figure to watch than earnings per share, and Amazon is doing quite well in that department. Operating cash flow grew 47% year over year, to $7.84 billion in the trailing-12-month period ended in March 31, 2015.

Also, the first quarter in 2015 was the first time ever that Amazon disclosed financial information for its Amazon Web Services cloud computing division, and the business looks remarkably healthy. Sales during the quarter were $1.57 billion, growing by an impressive 49% year over year, and producing $265 million in operating earnings during the period. Investors will most likely keep a close eye on Amazon's cloud computing business in the coming earnings release.

Andrés Cardenal owns shares of Amazon.com. The Motley Fool recommends Amazon.com. The Motley Fool owns shares of Amazon.com. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.