Undoubtedly the biggest concern among investors going into Apple's (NASDAQ:AAPL) earnings release on Tuesday is whether of not the tech giant's iPhone sales will be able to continue upward. While Apple CEO Tim Cook did imply during the company's fourth-quarter earnings call last year that he expects growth ahead for iPhone sales, some investors are worried that sales of its latest generation of iPhones may not be as robust as the company was expecting.

One of the catalysts Apple was counting on in 2016 to help drive more growth in iPhone sales was further growth in its Greater China, as well as its other emerging markets. Investors will get to check in on these catalysts for growth when the company reports results after market close on Friday to see if these growth drivers are living up to expectations.

Reviewing Apple's growth markets
Just how big of a growth driver are these markets for Apple? Consider some of these tidbits on Apple's emerging markets:

  • In Q4, Apple's Greater China revenue, which now represents about 24% of Apple's revenue, nearly doubled.
  • Apple's emerging-markets revenue, which also includes China, was up 65% in Q4 and now represents 31% of total revenue. This continued the company's 65% year-over-year growth in emerging markets in Q3.
  • iPhone sales in Mainland China were up 120% in Q4 compared to the year-ago quarter.
  • In Apple's third-quarter earnings call the company said iPhone sales in Korea and India were up 100% and 93%, respectively.

When Apple reports results on Tuesday, investors will get to see whether Apple's emerging markets are still serving up considerable growth for the company.

While Apple doesn't always provide specific data on emerging or even China specifically, it does always break down revenue for geographic segments it calls Greater China and Rest of Asia Pacific each quarter. For a point of comparison going into Q1's results, Apple's year-over-year revenue growth in Greater China and Rest of Asia Pacific in Q4 were 99% and 27%, respectively.

Investors shouldn't expect the same robust in these markets reported in fiscal 2015 in fiscal 2016. Decelerating growth rates will likely be evident in Apple's Tuesday release, as this is the first quarter the tech giant is up against the tough comparisons of it blockbuster iPhone 6 cycle. But considering Apple did expect overall growth in iPhone sales for the quarter, these markets should at last post some growth -- though it will probably be a notable deceleration from growth in fiscal 2015.

Looking ahead
Beyond checking in on the market's impact on Apple's results for the first fiscal quarter, investors will be just as interested in whether or not management believes these key markets can help the company post more growth in iPhone sales throughout the rest of the year. While Apple doesn't usually break down guidance by product or geography, the CEO may broadly discuss how he expects emerging markets to impact iPhone sales throughout 2016.

iPhone 6s. Image source: Apple.

Of course, Apple's overall revenue guidance for its fiscal Q2, too, could provide clues as to whether the company is expecting considerable growth from its emerging markets.

Investors can check in on Apple's growth in its emerging markets and on the company's guidance for Q2 by visiting Apple's investor relations page after market close on Tuesday, where a download of the company's quarterly results will be made available. Management will also probably share some useful insights about the performance of its different markets in its earnings call, which is scheduled for 5:00 p.m. ET.