Want another sign that Facebook's IPO hype has hit a new level? Analysts are already predicting that the tax bill for the Mark Zuckerberg's astronomic windfall will be something they've never seen before. CNN Money talked to analysts about the possible tax bill in a report out today. "I personally have never seen a bill into the billions -- close, but not quite," one analyst said. Here's how CNN did the math:

Facebook said in its IPO filing that it values its shares at $29.73. At that price, Zuckerberg's options windfall would be worth $3.6 billion. But analysts expect Facebook shares to go for a premium when they're sold to the public. A private-market trade last week valued Facebook's shares at $40 each -- giving the company an overall valuation of around $100 billion. That price tag would make Zuckerberg's options worth almost $5 billion.

Either way, the windfall lines him up for a whopping tax bill. The top U.S. marginal tax rate this year is 35%. Zuckerberg's home state of California also carves off a big slice, hitting those with incomes of $1 million or more with a 10.3% income tax.

For the full story head on over to CNN Money