iDevice maker Apple (NASDAQ:AAPL) is expected to report its earnings results for the fourth quarter of its fiscal 2015 and issue guidance for its fiscal first quarter on Oct. 27 after market close. Let's take a look at where current market expectations sit and what to keep an eye out for in the numbers and on the call.

It's been a crazy good year for Apple, but...
Fiscal 2015 has been nothing but incredible for Apple. During this year, the company has managed to deliver double-digit revenue and profit growth rates atop of what were already very large bases on both. This has been fueled by the, frankly, legendary iPhone 6/6 Plus product cycle.

With the iPhone 6/6 Plus, Apple not only tapped what turned out to be huge pent-up demand for larger-screen iPhones (catalyzing a significant upgrade cycle), but it also delivered a pair of products compelling enough to materially increase the rate at which people switched over from Android to iPhone.

It's really been a great year and a wonderful product cycle for Apple.

The problem, though, is that some investors are worried that Apple might not be able to grow its iPhone sales in the coming fiscal year.

Why guidance for the first quarter of fiscal 2016 will be key
Current Wall Street estimates are calling for Apple to guide to $77.05 billion in sales in the coming quarter, representing modest, albeit positive, year-over-year growth. Given how bullish analysts tend to be about Apple these days, I suspect that sentiment among money managers and shareholders is not as sanguine as that of Street analysts on average.

If Apple executives actually hit or even exceed the midpoint of current Street estimates, then I'd expect the shares to move appreciably higher from current levels. If Apple outright says that it believes organic demand for its iPhone 6s/6s Plus is greater than the demand that the company saw for the iPhone 6/6 Plus last year, then a swift move to fresh 52-week highs would not be out of the question.

However, if Apple issues weaker guidance than that the Street is looking for (particularly if that guidance suggests a year-over-year decline in iPhone unit shipments), then I'd expect analysts to take down their estimates for the full year. Given that stocks often trade based on forward estimates a year out, I'd expect the stock price to come down in that case.

A year in purgatory for shareholders?
If Apple starts fiscal 2016 off on a bad note, I suspect that the stock will be difficult to own throughout the entire iPhone 6s cycle. The device is its freshest in the fiscal first quarter and, due to typical seasonality, it's all downhill from there until the next iPhone launches.

The next real chance for Apple stock to become exciting again, in the case of a disappointing first fiscal quarter outlook, would seem to be the first weekend sales numbers that the company publishes following the unveiling of its next iPhone in September 2016.

If those numbers indicate organic year-over-year growth in iPhone demand, that may be taken as a signal by investors at that time that iPhone will return to growth. And, in that case, Apple stock would once again become exciting.

Check back here on Oct. 27 for my take on Apple's latest earnings report. And, if you're interested in my thoughts in real time on the earnings report and the conference call, be sure to follow me on Twitter. 

Ashraf Eassa has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Apple. 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.