So how much will Facebook CEO Mark Zuckerberg have to pay in taxes for taking his social network public?

According to a report in CNN, more than $1 billion. The reason for Zuckerberg’s hefty tax bill is linked to Facebook’s first day on Wall Street.

When Facebook’s initial public offering was introduced, Zuckerberg exercised an option to scoop up 60 million shares, the report says. That move counts as standard income in the eyes of the IRS, which would equate to about $2.3 billion.

Citing three certified public accountants based in California, CNN says Zuckerberg’s final tally, after deducting charitable donations, sits at $1 billion.

Zuckerberg should have no trouble clearing his tax bill. According to Forbes’ billionaires list, he’s worth $13.3 billion.