Google Inc. (NASDAQ:GOOG) Executive Chairman Eric Schmidt can begin selling this month about 42 percent of his shares in the company under a stock-trading plan adopted last November, according to a U.S. Securities and Exchange Commission Form 8-K filed Friday.

Under the one-year stock-trading plan, Schmidt intends to sell about 3.2 million shares of his Class A common stock, Google said in the filing. As of Dec. 31, he owned roughly 7.6 million shares of Class A and Class B common stock, the company said.

Schmidt's holdings at that time represented about 2.3 percent of Google's outstanding capital stock and about 8.2 percent of the voting power of the company's outstanding capital stock.

At Google's closing share price of $785.37 on Friday, Schmidt's sale of 3.2 million of the company's shares would produce about $2.51 billion, but, of course, the actual sales prices will vary over the coming year.

Schmidt served as Google's CEO from 2001 to 2011, when he stepped down and became the company's executive chairman. Google co-founder Larry Page replaced Schmidt as the company's CEO.

"The prearranged trading plan was adopted in order to allow [Schmidt] to sell a portion of his Google stock as part of his long-term strategy for individual asset diversification and liquidity," the company said in its SEC filing.

Schmidt is the third-largest stockholder among Google executives, behind only Page and co-founder Sergey Brin. Page owns an 8.7 percent stake, while Brin owns an 8.5 percent stake, the Associated Press reported.