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If and when Elon Musk sells a large chunk of his Tesla shares, it’ll probably have relatively little to do with a Twitter poll among his loyal followers — and everything to do with a looming multi-billion-dollar tax bill.

Musk published a Twitter poll over the weekend, noting that because he doesn’t receive a cash salary he pays income tax only when he sells shares. And because “much is made lately of unrealized gains being a means of tax avoidance,” he asked the Twitterverse if he should sell 10% of his shares. Some 58% of respondents said yes.

The tweet got attention, as many of Musk’s social media antics do. But the move is not really about a populist vote.

The real reason is because Musk is just months out from a deadline to exercise the stock options he received years ago. If he doesn’t use them, he loses them. And if he does exercise his shares, he’s going to face a monster tax bill between nearly $11 billion to as much as $16 billion at current share prices.

Continued increases in the value of Tesla stock could push his tax bill even higher. Shares of the EV maker, which rose 743% last year, are up another 68% so far this year — though they did drop 3% Monday following his weekend poll.

Musk received the 22.9 million stock options in question as part of his 2012 compensation package. Those options are due to expire August 13, 2022, making them worthless unless Musk exercises them before the deadline.

Once he exercises, however, those shares would be treated as regular income subject to income tax, said Mark Luscombe, principal federal tax analyst for Wolters Kluwer Tax & Accounting.

In most cases, options like these, which are based on hitting performance numbers, are taxable not as income but instead at the lower capital gains rate. But Musk would face the income tax rate because of a special rule: He owns more than 10% of Tesla’s total shares.

The taxable income is calculated based on the market value of the stock on the exercise date, minus the price paid to exercise the options. At Monday’s level, that taxable amount would be about $27 billion — and the top federal income tax rate is 37%, with another 3.8% net investment tax on top of that. So exercising would cost Musk nearly $11 billion today.

Musk owns 170.5 million shares of Tesla stock outright, and he has options to buy another 73.5 million as of today including the ones expiring next year. He’ll get even more if Tesla continues to grow and hits very achievable financial targets.

The value of those shares and options comes to nearly $300 billion, making him the richest person in the world, but an analysis by ProPublica in June found Musk paid no federal income taxes in 2018 — and in 2017 he paid only $65,000.

“Note, I do not take a cash salary or bonus from anywhere. I only have stock, thus the only way for me to pay taxes personally is to sell stock,” Musk tweeted on Saturday. In June he tweeted a response to a tweet about his tax bill, saying that the “only time I sell Tesla stock is when my stock options are expiring & I have no choice.”

State taxes could add to his tax bill

Musk may also face state taxes on top of the federal bill.

He did move his residence from California to Texas, which has no state income tax, compared to California’s top rate of 13.3%. He has announced plans to also move Tesla’s California headquarters to Texas.

But he could be hit with at least some California state income tax, given that Tesla still has a major factory and offices in California and Musk still spends time working there. Musk acknowledged that in the June tweet: “Btw, I will continue to pay income taxes in California proportionate to my time in state, which is & will be significant.”

It’s not clear what the final state tax bill would come to, as California may or may not try to tax all of Musk’s proceeds from these expiring options since almost all of Tesla’s operations were in the state when the original grant was made. An additional 13.3% state income tax would come to $3.6 billion.

It’s also possible Musk will receive additional options to buy 2.6 million more shares from that 2012 grant. Those options could be worth another $3 billion if he gets them by the August 2022 expiration date.

A major stakeholder announcing plans to sell shares is rarely a good thing for a stock. But many analysts are still bullish on Tesla, predicting further price increases in the year ahead. Investors were already pricing in some stock sales by Musk due to the expected tax bill, said Daniel Ives, senior equity research analyst at Wedbush Securities.

“With a tax bill that we calculate at north of $10 billion, selling stock over the coming months is not a surprise,” Ives wrote in a note to clients Monday, “although holding a Twitter poll to sell 10% of his stock is another bizarre soap opera that can only happen to one company and one CEO in the world.”

– CNN Business’ Ramishah Maruf contributed to this report