Apple's market capitalization has dropped by roughly $90 billion since July 20, Business Insider reports. That $90 billion figure is based on Apple's opening stock price of $130.97 on July 20 and its current number of outstanding shares, which is 5.77 billion.

At its highest, Apple's market cap surpassed $765 billion earlier this year in February. Apple's current market cap now sits at $656.21 billion.

It's unclear exactly what caused the slip in Apple's stock, but Bank of America Merrill Lynch recently downgraded Apple stock from "Buy" to "Neutral" with a new stock-price target of $130 from $142.

Analysts have been concerned about Apple's reliance on the iPhone, whose sales are slowing, and think it will be hard for Apple to grow its smartphone market share in China — last quarter, Apple's share slipped into third place behind Xiaomi and Huawei, according to Canalys.