For many investors, a day in late January resembles the Super Bowl of all earnings reports. We're talking Apple's (NASDAQ:AAPL) first-quarter earnings report, of course.

Apple has been one of most closely watched companies on the Street for years. Investors everywhere tune in to see how the world's most valuable publicly traded company performs each quarter, particularly the holiday quarter; the tech giant's first fiscal quarter of every year, which is the fourth calendar quarter, is almost always the tech giant's biggest quarter of the year.

So, mark your calendar. The California-based technology company has just put a date on its earnings release: Jan. 26. 

Here's an early preview of what investors will want to watch when the company reports first-quarter results.

Leading up to Apple's first-quarter earnings release, analysts are, on average, expecting the company to report revenue and EPS of $77.1 billion and $3.25 per share, respectively. This compares to revenue and EPS of $74.6 billion and $3.06 per share in the year-ago quarter.

If Apple were to achieve these expectations for revenue and EPS, the company's revenue and EPS would be up 3.4% and 6.2%, respectively.

One key focus when the company reports results will be revenue. The middle of Apple's guidance range for revenue suggests management expects Q1 sales to increase only about 2.5%. This would be a notable slowdown for the company considering its year-over-year revenue growth has been 22% or higher during the last four quarters.

Investors may have higher expectations for the tech giant's revenue than analyst estimates suggest. Apple's revenue in the year-ago quarter absolutely crushed estimates. Analysts expected about $67 billion in revenue during quarter and the company instead raked in around $75 billion.

iPhone sales
Another metric investors will undoubtedly be watching closely when the company reports first-quarter results is iPhone sales. Now accounting for about 63% of the company's revenue, the segment's performance is more important to Apple's overall results than ever.

iPhone 6s. Image source: Apple.

During the year-ago quarter, Apple sold a whopping 74.5 million iPhones -- far more than analysts were expecting. Benefiting from pent-up demand for Apple phones with larger screens, the iPhone 6 sparked a wildly successful upgrade cycle for the company. The 74.5 million iPhones shipped during the quarter represented 46% year-over-year growth in iPhone unit sales. Outdoing last year's holiday quarter isn't going to be easy.

For Apple to be able to achieve the revenue it has guided for, the company is probably going to need to sell at least as many iPhones as it sold during the record year-ago quarter.

Apple's first-quarter financial results will be released after market close on Tuesday, Jan. 26. Investors will have an opportunity to tune into the company's live conference call at 5:00 p.m. ET.

Stay tuned at The Motley Fool for more pre-earnings Apple coverage, as well as analysis of the quarter's results when they are available.