Where Elon Musk might find the cash to buy Twitter

• Tesla and SpaceX CEO Elon Musk announced a surprise bid to buy Twitter at a $43 billion valuation.
• His offer has one major issue: It would require Musk to come up with roughly $40 billion in cash.

Twitter's largest shareholder, Elon Musk, offered to buy the rest of the social media platform on Thursday for $54.20 per share in a deal that valued the company at $43 billion.

"Twitter needs to be transformed as a private company," the Tesla and SpaceX CEO said in a letter to Twitter's chairman, Bret Taylor. "Twitter has extraordinary potential. I will unlock it."

The offer represents a premium of more than 50% above the stock's price at the end of January, when Musk began quietly acquiring shares, but substantially less than the 52-week high of $73.34.

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Musk's current stake in Twitter represents about 9.2% of the company, worth roughly $3.3 billion, which leaves nearly $40 billion needed to complete the deal.

That's a lot of cash — even for the world's wealthiest man.

Like most billionaires, the majority of Musk's fortune is tied up in equity in his companies, namely about 17% of Tesla's publicly traded stock and an estimated 40% of privately held SpaceX. Neither of those would be particularly reasonable to sell in order to fund the purchase of Twitter.

A tally by Reuters estimates Musk raised about $16.4 billion in cash last year from his sale of Tesla stock last year.

After expenses like taxes and buying his current Twitter holdings, Bloomberg estimates his current cash accounts to be worth $2.95 billion.

Another option that Musk is known to take advantage of is pledging his Tesla shares as collateral for a loan. Bloomberg notes there is a limit of 25% of the shares' value, which could put him in the neighborhood of $40 billion if he chooses to maximize that option.

There's also the possibility that Musk finds an investing partner willing to foot a portion of the bill to help advance Musk's agenda of making Twitter "the platform for free speech around the globe."

All of this is, of course, contingent on Twitter's board actually accepting Musk's offer, an outcome that is at this moment wildly uncertain at best.