New York CNN Business  — 

Elon Musk has gotten a lot of attention from buying a 9.1% stake in Twitter, along with landing a seat on the company’s board. He’s also worth an additional $1 billion.

In a new filing late Tuesday, Musk disclosed how much he paid for the 73 million shares he started purchasing in late January and completed with a final buy Friday. The average price was $36.16 per share.

The news of his Twitter investment sent shares up 27% Monday, and another 2% by Tuesday’s close, before slipping slightly in Wednesday trading. But even with that step back in price, Musk is looking at an on-paper profit of roughly $1.1 billion on his $2.6 billion investment. That equates to a return of about 40%. Not bad for a two-month investment.

Of course, that amount is essentially sofa cushion change for the world’s richest human being. Musk’s initial investment represented less than 1% of his net worth, which Forbes estimates at $282 billion. A $1 billion profit? Call it a rounding error.

In fact Musk disclosed on Twitter Wednesday that he had made an error in his initial filing that showed he had purchased 73.5 million shares, which works out to a 9.2% stake in the company.

His filing Tuesday night disclosed the correct number of shares: 73.1 million shares, or a 9.1% stake. When some took that to mean he had already sold nearly 400,000 of those initial 73.5 million shares, he responded that the difference was due to a filing mistake.

As for how little a $1 billion profit might mean to someone as rich as he is, here’s some context: The Federal Reserve estimates that the US median household net worth is $121,700. So if a typical family had the same percentage increase in their net worth that Musk just got from his Twitter windfall, it would total $461. Not exactly earthshaking.

So given his vast wealth, it’s fairly safe to say that no person on the planet has ever needed an extra $1 billion less than Elon Musk.