Facebook CEO Mark Zuckerberg will sell up to 75 million shares of Facebook over the next 18 months, he said in a post on Friday.

At the current Facebook share price of $170, that means Zuckerberg could sell up to $12.7 billion in Facebook stock.

He could also sell as few as 35 million shares of Facebook, which would work out to just under $6 billion in Facebook stock.

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Zuckerberg is selling some of his Facebook shares to fund the Chan Zuckerberg Initiative, the philanthropic organization he formed in late 2015.

He also announced that Facebook is withdrawing a proposal to reclassify its stock to create a class of non-voting shares. He explained that because Facebook’s share price has increased recently, he can sell some of his stock and continue to retain control of the company he founded.

Zuckerberg plans to give away 99% of his Facebook shares during his lifetime, valued at about $70 billion.

Here’s his full note: 

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