Amazon.com (NASDAQ:AMZN) should be reporting its third-quarter results in just four weeks from this week. While no firm date has been announced, various sites peg the e-commerce behemoth's report date as Wednesday, Oct. 23, or Thursday, Oct. 24. It seems probable that it will be the latter, as the company has reported its Q3 results on a Thursday for at least the last three years.

Investors will likely be approaching the report with more uncertainty than in the recent past. Last quarter, Amazon's earnings fell short of Wall Street's consensus estimate, breaking a five-quarter string of expectation-crushing earnings.

Shares are up 19.5% so far in 2019 through Friday, Sept. 20, slightly trailing the S&P 500's 21.1% return. The stock, however, remains one of the best long-term performers among both tech and consumer goods stocks.

Here's what to watch when Amazon reports.

Key numbers

Metric Q3 2018 Result Amazon's Q3 2019 Guidance Amazon's Projected YOY Change Wall Street's Q3 2019 Consensus Estimate Wall Street's Projected YOY Change Revenue $56.58 billion $66 billion to $70 billion 17% to 24% $68.82 billion 21.6% Adjusted earnings per share (EPS) $5.75 N/A N/A $4.53 (21.2%)

For Q3, Amazon expects operating income in the range of $2.1 billion to $3.1 billion, representing a decline of 16% to 43% from the year-ago period. The projected drop is anticipated to be driven by the company's plan to continue spending on upgrading Amazon Prime's core free delivery benefit from two days to one day. On last quarter's earnings call, CFO Brian Olsavsky said spending on this initiative is expected to accelerate from Q2's level, which he disclosed as being somewhere a little higher than $800 million.

Amazon Web Services' overall growth

Beyond the headline numbers, a key thing to focus on is AWS' overall growth, as this segment has historically been the company's earnings-growth engine. While Amazon's cloud service remains fast-growing and very profitable, last quarter's results probably came in somewhat lighter than what many investors were expecting.

In Q2, the segment's revenue grew 37%, but operating income grew "only" 21%, resulting in an operating margin of 25.2%. This metric is down from 28.9% in the first quarter and 29.3% in the fourth quarter of 2018.

Signs the Prime delivery upgrade is boosting North America's growth

While it's still early, we'd like to see signs that the company's spending on increasing its Prime delivery speed will pay off. Last quarter, Amazon's largest segment grew revenue 20% year over year to $38.7 billion, but operating income fell 15% to $1.56 billion, which was about 50% of total operating income of $3.1 million. The drop was largely due to spending on the Prime delivery upgrade previously described.

Q4 2019 guidance

The market's reaction to Amazon's upcoming report will probably hinge more on the company's Q4 guidance than on its results for Q3. (Amazon provides an outlook for revenue and operating income but not for earnings.)

So, you should know Q4 expectations: Wall Street is modeling for revenue to jump 20.7% year over year to $87.37 billion and adjusted earnings to rise 6.3% to $6.42 per share.