According to MarketWatch, Apple surpassed Microsoft with a float-adjusted cap of $241.5 billion. Those numbers do not use the full market basis, but apply only to shares on the open market.
Apple's total was larger than Microsoft's index market value of $239.5 billion on the Standard & Poor's. However, in terms of total actual market cap, Apple remains well below Microsoft, with a difference of more than $30 billion. Previously, a number of outlets, including MarketWatch, had incorrectly reported that Apple's total market cap had surpassed Microsoft.
The milestone came after Apple announced on Tuesday that its profits increased nearly 90 percent year over year, thanks to strong Mac and iPhone sales.
Exxon still remains the top company on the S&P 500., with a market cap of $324 billion. Earlier this year Apple moved past Berkshire Hathaway and Walmart to become the third-largest U.S. company in terms of market cap.
The numbers could change quickly, though, with Microsoft announcing its earnings Thursday afternoon. Apple's stock increased $7.25, or 2.8 percent, in trading on Thursday to propel it past Microsoft. AAPL is also significantly up from its 52-week low of $119.38.
Apple's growth has been largely credited to the company's CEO, Steve Jobs. In December, the Apple co-founder was named the world's best-performing CEO for increasing his company's market cap a whopping $150 billion over a 12-year span.