Tuesday night, Elon Musk made a bold statement on Twitter: That he would pay more taxes than any American in history this year.

Musk may be right. The eccentric billionaire (and the richest person in the world) probably owes the federal government at least $ 8.3 billion by 2021, Forbes estimates, based on its stock sales of nearly $ 13 billion through Dec. 13. Amazon founder Jeff Bezos came close last year, selling his company’s stock for $ 10.2 billion; the tax bill for this could have reached $ 2.4 billion. However, only the Internal Revenue Service knows who is the biggest taxpayer in American history.

More key context: In some previous years, Musk paid little to no taxes. According to a ProPublica published survey in June, Musk paid a total of $ 455 million in federal income taxes between 2014 and 2018, while his wealth increased by $ 13.8 billion; Musk paid no federal income tax in 2018. (He also didn’t sell Tesla shares that year.)

It’s possible that he has other sources of income that will boost his 2021 score, or that he uses trade losses from elsewhere in his holdings – a common tactic among the super-rich – to lower his bill. Musk also sold half a dozen California mansions this year, which likely generated taxable income.

Musk dodged a costly bullet in October, when Sen. Ron Wyden (D-Ore.) Presented a short-lived plan that would have taxed unrealized capital gains from America’s richest people, who Forbes the estimates could have cost Musk $ 29.8 billion. But within days, the plan was replaced by a less drastic measure. Because Musk currently does not receive an annual salary from Tesla and the company does not pay any dividends, Musk likely should not have owed Uncle Sam any taxes – until he started offloading Tesla shares to a unprecedented pace from November.

His tax bill could be even higher if California goes after him. Although Musk moved to Texas last year, his former home state could tax Musk on the value of options he earned while residing there. Between state and federal taxes, Musk could end up with an overall tax rate north of 50%. (Although some types of options can be exercised without triggering immediate taxes, and the proceeds from the sale of shares are taxed at lower rates of appreciation, Musk’s stock options are “Unqualified,” meaning they will likely be subject to the much higher regular tax rate imposed on offsets, according to the tax lawyer and Forbes contributor Bruce Brumberg.)

Musk could lower his tax bill this year if he donates Tesla shares – or cash – to his Musk charitable foundation or directly to one or more nonprofits. Taxpayers who itemize donations can deduct certain charitable donations from their adjusted gross income. Based on a reading of documents filed with the Securities and Exchange Commission, Musk has only donated Tesla shares so far in 2021; the last time he did so was in December 2019, when he invested 11,000 Tesla shares, then worth $ 4.1 million, in his foundation.

The tax authorities have not yet finished. Another $ 7 billion in federal taxes could await Musk if he keeps his recent promise to sell 10% of his Tesla shares. (So ​​far he has sold about 3.2% of his stake.) He is expected to pay the IRS about $ 2.65 billion in additional capital gains taxes based on the share price. Tesla stock on Dec.15, plus an additional $ 4.4 billion if he exercises the rest of his capital. the stock options will expire in August 2022 – if the Tesla share price stays the same. It is not obvious; stocks are down nearly 22% from their high of $ 1,222 on November 1, 2021.

Musk’s tweet on Tuesday was part of a tirade against Senator Elizabeth Warren (D-Mass.), The latest installment in his social media feud against progressive politicians. After Sen. Warren tweeted calling for a change to the “rigged tax code” to force Musk to “actually pay taxes and stop picking on everyone,” Musk responded with chutzpah: ” Please don’t call the manager on me, Senator Karen.

On Monday, Time Magazine named Musk “Person of the Year,” triggering Senator Warren’s tweet about the CEO’s tax obligations.

Musk did not immediately respond to Forbes’ request for comments on their tax bill.