Like clockwork, Apple's (AAPL 1.27%) stock is trending upward in anticipation of the next-generation iPhone launch. But the pressure going into this year's launch is undoubtedly greater than the pressure going into the iPhone 5s launch. Apple stock is trading about 5% off its all-time high just over a post-split $100 a share, and about 19% higher than at any point in 2013.

4.7-inch and 5.5-inch iPhone 6 mockups pictured with the 4-inch iPhone 5s. Source: 9to5Mac, used with permission.

And just as has been the case for several years, Apple's reliance on iPhone sales for its business results is enormous. In the company's most recent quarter, iPhone sales accounted for 57% of total revenue. And, based on comments from Apple about how its gross profit margin is affected by product segments, we also know that its iPhone segment boasts higher gross profit margins than other segments. In short, Apple's iPhone business is absolutely essential to overall business performance.

When can investors expect the iPhone 6 to be announced? The first or second week of September is looking likely now, according to MacRumors (citing a "reliable source").

But this comes as no surprise, MacRumors' Juli Clover explains.

An early September event is in line with previous rumors and with the event dates of the last two iPhone generations. The iPhone 5 was announced on Wednesday, September 12 with availability occurring on September 21 and the iPhone 5s/5c was announced on Tuesday, September 10, with availability starting on September 20. 

The iPhone 6 will mark a major departure in terms of design, with both a sleeker form-factor and models with larger displays. The next-generation iPhone will allegedly come in two versions: a 4.7-inch display size and one with a phablet-like 5.5-inch display.

iPhone 6 concept. Design by Tomas Moyano and Nicolas Aichino.

The iPhone 6: A blockbuster hit?
The iPhone 6 looks poised to be a winner in the market.

Given the fact that there's likely meaningful pent-up demand worldwide for an iPhone with a new form-factor and larger display, carriers are poised to have an unusually large number of subscribers eligible for upgrades at the time of launch, and that China Mobile's (the world's largest carrier) LTE rollout will be in full swing, it's reasonable to expect iPhone unit sales in fiscal 2015 to be around 20% greater than in fiscal 2014.

At this rate of growth for Apple's most valuable segment, 15% EPS growth in fiscal 2015 is downright conservative -- especially after you take into consideration Apple's aggressive share repurchase program.

4.7-inch and 5.5-inch iPhone 6 mockups pictured with the 4-inch iPhone 5s. Source: 9to5Mac, used with permission.

Most important of all, the iPhone has served as an excellent gateway device for new Apple customers. And given the strength and "stickiness" of Apple's ecosystem, once Apple gets new customers using its products, customers often buy other products and continue to upgrade to new devices. And for customers who are already using the iPhone that decide to upgrade, the iPhone 6 will only get them even more entrenched in the ecosystem.

So though the iPhone 6 may only be the major driver for Apple sales in one fiscal year, the growth in customer base that could result is likely to have lasting effects for Apple's business.

Just about two months out from the rumored launch, we'll soon get to see the iPhone 6's impact on the business first hand. But considering the conservative valuation for the stock, I wouldn't wait until after fiscal 2015 passes to buy in to the opportunity.