For the 21st year in a row, Microsoft (NASDAQ:MSFT) co-founder Bill Gates topped the Forbes list of the wealthiest Americans. Gates now has an estimated net worth of $81 billion, putting him well ahead of his runner-up and good friend, Warren Buffett, who has an estimated $67 billion net worth.

Here's the thing: Gates makes more in a single day doing nothing than the average person makes in a lifetime. By a long shot.

Bill Gates stills owns tons of Microsoft shares
For the longest time, Gates was the single largest individual Microsoft shareholder. Earlier this year, he passed that title to his longtime friend and CEO successor, Steve Ballmer, who himself resigned as CEO earlier this year. Still, as of Gates' most recent SEC Form 4 disclosure, he still owns nearly 298 million shares of Microsoft. (This doesn't include the 425,000 shares that his wife, Melinda Gates, owns.)

The software giant has just increased its quarterly dividend to $0.31, or $1.24 per share per year. That puts Gates' annual dividend income from his Microsoft position at a whopping $368 million. That translates into just over $1 million per day. Gates doesn't have to do anything other than hold his shares to earn that money. Additionally, this doesn't include Gates' investment income, interest income, or various other forms of compensation.

Bill Gates is actually selling his shares
Many years ago, Gates actually set up a prearranged 10b5-1 trading plan to slowly cash out his sizable holdings in the company he founded. Gates sells approximately 20 million shares per quarter. That's why Ballmer is now Microsoft's largest individual shareholder, with over 333 million shares.

At this rate, Gates will sell all of his holdings by mid-2018. That means that over time, Gates' annual dividend income will also decline, but I don't think he'll have any trouble paying his electric bill anytime soon.

Bill Gates doesn't do nothing 
Most importantly, just because Gates doesn't have to do anything doesn't mean he isn't doing anything. Quite the contrary.

While Gates officially transitioned away from daily operations back in 2008, he continued to serve as chairman of the board for many years. When Microsoft named Satya Nadella as its new CEO earlier this year, it also said Gates would assume a new role as technology advisor, helping Nadella with product decisions while relinquishing the chairman title. Gates said Nadella asked him to "pitch in," and Gates is expected to take a more active role at the company again as a result.

But the bulk of Gates' time these days is spent pursuing philanthropic endeavors through the Bill & Melinda Gates Foundation. Through the Foundation, Gates is able to tackle humanity's most challenging problems. Few people in the world have the wherewithal to fight malaria and poverty on such a massive scale, and there's perhaps no better person to responsibly and generously dedicate such a fortune to helping mankind.

Evan Niu, CFA has no position in any stocks mentioned. The Motley Fool owns shares of Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.