$4.6 billion, to be exact. According to a Securities & Exchange Commission filing released on Monday and picked up by Bloomberg, Gates donated 64 million shares of Microsoft on June 6. The report notes that this is the billionaire’s largest donation since 2000, when he donated stock valued at $5 billion to create the Bill & Melinda Gates Foundation.

While the SEC filing did not specify the gift’s recipient, it is expected that the money will go to Gates’ charity. The Chronicle of Philanthropy estimates that this would bring the total of Gates’ donations to the foundation to more than $18 billion.

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As a co-creator of the Giving Pledge with Warren Buffett, Gates has committed to giving a majority of his wealth to charity. His latest donation represents 38% of his Microsoft holdings (his stake is now down to 1.3% from 24% in 1996), but it’s still only a small fraction of his total wealth, estimated at over over $85 billion by Bloomberg. Not including this latest donation, the foundation currently has an endowment of $40.3 billion—augmented in no small part by a $36.1 billion donation made by Buffett in 2006.