New iPhones expected from Apple on Wednesday come amid questions about whether the company can sustain growth for its best-selling device.
Apple sold more than 74 million iPhones in the first three months after it released the super-sized iPhone 6 and 6 Plus models last year. That's 46 percent more phones than it sold in the same period a year earlier. To get that same 46 percent increase, Apple would have to sell more than 108 million iPhones in the next three months.
Jerry Kim, a Columbia University management professor, says the expectations might seem unfair, but Wall Street "will definitely be disappointed if they can't break another record next quarter."
Apple CEO Tim Cook has said he believes there is still room for iPhone sales to expand. He's told analysts that an increasing number of iPhone buyers are people who used to own devices running Google's Android software.
Research firm Kantar Worldpanel says many iPhone owners have older models, suggesting they may be ready to upgrade to a newer iPhone in the coming months.