Mark Zuckerberg
Facebook CEO Mark Zuckerberg had a lot smile about as he raked in a cool $1 bn on his birthday. Reuters

Mark Zuckerberg had a lot to smile about as he celebrated his 31<sup>st birthday.

Facebook's shares jumped from $2.93 to $81.37, making for a billion dollar birthday payout for the founder and CEO of the social networking site.

According to USA Today Money the stock's rise saw his 426.3 million shares jump $9.4bn (£6bn) in value in addition to his $610,455 annual salary.

And while he has an estimated net worth of $35bn, Zuckerberg, who owns 15% of Facebook's shares, was content with a low-key celebration with his wife Priscilla.

I'm a low-key birthday person. I get too much attention the rest of the time.
- Mark Zuckerberg

Speaking at a town hall question and answer session at the Menlo Park, California headquarters, he said: "I'm a low-key birthday person. I get too much attention the rest of the time."

Explaining why he was not a fan of an extravagant celebration, the entrepreneur shared a story from his 30th birthday. He revealed that he had tried to escape any celebrations by flying across the country. However, when he returned to work he found a conference room filled with birthday balloons.

In a rare act of defiance, Zuckerberg held all his meetings there for the rest of the day including one where the CEO had to remonstrate some of his employees telling them that had to do "better work" and that they were letting "our community down".

"We were all up to our waists in balloons, and everyone was just so sad," he said "It was ridiculous."

Commenting on his preference for wearing the same grey T-shirt and hoodie, Zuckerberg described his style philosophy as anything that wouldn't require him to "spend a lot of time thinking about fashion."

Asked what he would wear when he turns 80, he replied: "Maybe I'll wear like a unitard. A onesie? Who knows what kind of incredibly unfashionable thing I'll have found."

Mark Zuckerberg was voted 16th in Forbes' World's billionaires list.