It's that time of the year again when Apple (NASDAQ:AAPL) brings the spotlight to earnings season. The world's most valuable publicly traded company is scheduled to report its fiscal fourth-quarter results on Thursday, Nov. 2.

Following the introduction of the new iPhones and updated versions of its Apple Watch and Apple TV, investors will have a lot of questions. Hopefully, the quarterly update will provide some answers.

Here are three key metrics investors should check on after Apple's fourth-quarter numbers go live.

iPhone 8 and 8 Plus being splashed by water

Released nine days before the quarter's close, the iPhone 8 and 8 Plus will play a key role in Apple's fourth-quarter results. Image source: Apple.


As usual, total revenue will be an important metric to watch. Apple investors are particularly sensitive to the tech giant's revenue trends as it was only the first fiscal quarter of this year when the company returned to revenue growth after suffering a period of decline.

AAPL Revenue (Quarterly YoY Growth) Chart

AAPL Revenue (Quarterly YoY Growth) data by YCharts.

For its fourth quarter, Apple guided for revenue to be between $49 billion to $52 billion. This compares to revenue of $46.9 billion in the year-ago quarter. So, the midpoint of its guidance calls for year-over-year revenue growth of 7.7%, slightly better than the 7% year-over-year revenue increase in Q3.

Given that Apple's guidance typically proves to be conservative, investors should look for fourth-quarter revenue to be at the high end of this range.

iPhone sales

Since iPhone accounts for over half of Apple's revenue, guidance for total revenue growth implies that management also likely expects growth in iPhone revenue. But some analysts have expressed concerns about iPhone sales during the quarter since the flagship iPhone X isn't available until November.

But I suspect management had enough visibility into its supply chain to anticipate a delayed iPhone X launch. In other words, I believe Apple's revenue guidance for the quarter already takes into account the timing of the iPhone launch. So, management likely expected revenue from its new iPhone 8 and 8 Plus to contribute enough during the quarter for the company to grow iPhone revenue on a year-over-year basis -- without the help of iPhone X.

I'm expecting low single-digit revenue growth from the iPhone, with Apple's services and other products segments playing a meaningful role in helping to achieve its guidance for overall revenue.

In Apple's fourth fiscal quarter of 2016, iPhone revenue was about $28.2 billion. This quarter, look for it to be close to $29.3 billion, up about 4% year over year.

Gross profit margin

Apple's gross profit margin comes back into the spotlight every year after an iPhone launch. Some iPhone models have higher initial costs than other iPhone models, so it's interesting to see how new iPhones are impacting overall profitability. While the iPhone 8 and 8 Plus were only available for nine days during the quarter, they could have some influence on the company's gross profit margin.

Fourth-quarter gross profit margin is expected to come between 37.5% and 38%. This compares to a gross margin of 38% in the year-ago quarter.

But the most interesting aspect of Apple's fourth-quarter earnings release to watch when it comes to gross profit margin is the guidance for its first-quarter gross profit margin. Since the iPhone X is scheduled to launch on Nov. 3, investors will likely see management's expectations for the phone's profitability reflected in the gross profit margin guidance for the first quarter of fiscal 2018. For a benchmark, Apple's gross profit margin in its first quarter of fiscal 2017 was 38.5%.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.