Mark Zuckerberg will sell a large number of Facebook shares over the next 18 months in sales that would be worth between $6 billion and $12.8 billion based on the stock's current price.

The intention to sell between 35 million and 75 million shares was disclosed in a Facebook securities filing late Friday.

Proceeds of the sale will go "to fund the philanthropic initiatives of Mr. Zuckerberg and his wife, Priscilla Chan," the filing said.