After iPhone X, what’s next for Apple Inc. stock?

Now that Apple (NASDAQ: AAPL) has finally announced its highly anticipated iPhone X smartphone, current and potential investors in Apple are probably keenly interested in where the stock will head from here.

As of this writing, "here" means about $159 per share -- just a few bucks down from the all-time high of $164.94 that the shares hit less than a month ago.

So, does Apple stock stay flat, go up, or go down from here? Well, the answer to that, unfortunately, isn't that simple or clear-cut.

What will drive Apple stock?

Based on the big run that Apple's shares enjoyed ahead of the iPhone X launch, it's clear that investor expectations for the sales performance of the iPhone X are quite high.

Put another way, it'll take quite a lot for investors to be positively surprised at this point.

The new phones start at $999 for the base 64 GB model and go to $1,149 for the version with 256 GB, so right off the bat, Apple should enjoy a significant bump in iPhone average selling prices for the coming cycle.

Assuming even flat unit shipments year over year, a significant increase in iPhone average selling prices should translate into nice revenue growth.

All this is already known, so Apple simply delivering solid iPhone revenue growth in the coming quarters won't necessarily be enough to push the stock higher. Virtually everyone's already expecting some level of growth.

Indeed, if we look at current analyst estimates, we see that analysts are, on average, expecting Apple to enjoy 15.7% year-over-year revenue growth during Apple's coming fiscal year, with earnings per share surging about 21% over that same period.

Considering this, here's my thinking about what could drive Apple stock up or down, or cause it to trade sideways.

If it becomes clear that analysts have significantly underestimated the strength of this iPhone product cycle (this would become evident once Apple reports financial results for the first quarter of its coming fiscal year) -- I think analysts are correctly factoring in a large bump in iPhone average selling prices, but they don't appear as optimistic on unit shipment growth -- then expect analysts to revise their estimates for fiscal year 2018 (and probably beyond) upward.

Such upward revisions could very well push the stock to new heights.

However, if it looks as though analysts mostly got it right, then I'd expect the stock to trade sideways or, perhaps, slightly down as I wouldn't be surprised if the current share price reflects investor enthusiasm that's generally a bit greater than analysts'.

And, finally, if it turns out that the new iPhones aren't selling as well as expected (keep an eye out for reports from credible news sources about potential iPhone production cuts), then that could dramatically dampen enthusiasm for Apple stock and its prospects.

Remember that the iPhone X is supposed to represent the biggest leap that Apple has made in the iPhone in a very long time; if this product doesn't perform well in the marketplace (that is, help drive Apple's iPhone business at least to record revenue levels), then that could very well drive significant selling in the stock.

The broad thinking in this case may very well be something along the lines of, "If the iPhone X can't drive the iPhone business to record unit shipments and revenue, then nothing will."

Indeed, in this case (which I think is unlikely but not impossible), not only would estimates and general investor enthusiasm for this product cycle come down, but that pessimism wouldn't be isolated to estimates for fiscal 2018 -- it would be felt in both analyst estimates and investor expectations for many years to come.

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