Apple (NASDAQ:AAPL) stock continued its march higher on Tuesday, bringing shares to a new all-time high just over $163. The stock's gain follows a bullish forecast for iPhone sales thanks to the highly anticipated 10th-anniversary iPhone, which is rumored to launch next month.

But is the stock getting ahead of itself? Probably not -- and IDC's outlook for Apple's iPhone shipments in 2018 helps show why.

Two people standing outside of an Apple store at dusk.

Image source: Apple.

Here comes the growth

The impressive value in Apple stock, even after a 53% run-up in the past 12 months, is most evident when investors consider how significantly a game-changing 10th-anniversary iPhone update can affect the tech giant's finances.

To put this in perspective, consider how IDC's forecast for iPhone shipments could affect Apple's business.

The expected "iPhone 8" and Apple's rumored new iPhone 7s and 7s plus "will spur a major upgrade cycle" in 2017, IDC said in its report. Specifically, IDC forecasted "9.1% growth in [iPhone shipments in] 2018 with the iPhone 8 and the new 7S/7S+ models playing a pivotal part in the near double-digit growth next year."

With iPhone accounting for about 63% of Apple's trailing-12-month revenue, the product segment typically plays an integral role in the direction of the tech company's top line trends. Combining the iPhone's large share of Apple's total revenue, the iPhone 8's expected higher price tag, and the iPhone's ability to help drive sales growth in Apple's services segment, 9.1% growth in unit shipments in 2018 could mean Apple sees similar growth in its overall revenue during the year.

How would 9.1% growth in iPhone shipments impact EPS growth? While Apple's costs associated with manufacturing an entirely new form-factor for its flagship product could weigh on profitability in 2018, Apple's aggressive share repurchase program could offset any pressure this might put on EPS, ultimately helping Apple achieve around 9% year-over-year growth in EPS next year, too.

This scenario could give Apple EPS of about $9.60 next year, meaning the stock would be trading at 17 times Apple's 2018 earnings -- an extremely conservative valuation for a market leader that also boasts two rapidly growing business segments, services and other products, poised to continue growing strongly for years to come.

Sure, this is a ballpark scenario, but the underlying assumptions are reasonable enough to speak to the iPhone's potential to give Apple's business a big boost in the coming years.

Why betting on iPhone growth makes sense

Of course, some investors may believe it's risky to bet on iPhone growth. But there's good reason to believe an overhauled iPhone could be a major catalyst for Apple.

A jet black iPhone 7

iPhone 7. Image source: Apple.

It's been three years since Apple's last major form-factor update to the iPhone. And Apple's last big upgrade to its iPhone, which occurred when Apple made its first foray into larger smartphone displays with its iPhone 6 and 6 Plus, sparked a monster upgrade cycle. Thanks to Apple's iPhone 6 and 6 Plus launch, Apple's iPhone unit sales and revenue in fiscal 2015 surged 22% and 28%, respectively.

Sure, investors shouldn't automatically assume Apple can post similar growth this time around. But this is the first time ever that Apple has waited three years to debut a new form factor for iPhone. Further, beyond the expected form-factor overhaul, significant new technology in the device should help drive sales.

Even the mostly low-tech investor Warren Buffett seems to understand that plenty of consumers seem to be waiting for the latest and greatest iPhone. "A lot of people are waiting," he said in an interview about Apple with CNBC.

All of these factors -- IDC's reasonable forecast, Apple's pricing power, pent-up demand for an overhauled iPhone design, and the company's promising growth in its services and other products segments -- make Apple stock a buy today, even at an all-time high of $163.

Daniel Sparks owns shares of Apple. The Motley Fool owns shares of and recommends Apple. The Motley Fool has a disclosure policy.