Image source: Facebook.

If Mark Zuckerberg wasn't planning to give away 99% of his family's Facebook (NASDAQ:FB) shares before he dies, I bet he'd be a trillionaire at some point in his life. For now, though, he'll have to settle for a net worth of $51.7 billion, according to Bloomberg's Billionaire Index. That's up $5.9 billion year to date as of this writing.

His wealth increase was driven by his 14% stake in Facebook. The stock price increased a solid 13.5% so far this year, although it was up more than double that amount at one point this year. Those gains were offset by the sale of some of Zuckerberg's stock to fund the Chan Zuckerberg Initiative, the vehicle through which Zuck plans to donate 99% of his stock.

Facebook's revenue and earnings growth didn't slow down

Throughout 2016, Facebook consistently posted earnings results that beat analysts' expectations. Over the last four quarters, Facebook grew its revenue 55% to $24.7 billion. What's more, its net income grew a whopping 165% to $7.5 billion.

Those strong results were fueled largely by continued user growth, increases in engagement, and more advertising in Facebook's News Feed and Instagram.

Monthly active users (MAUs) increased from 1.55 billion at the end of the third quarter last year to 1.79 billion today. Daily active users (DAUs) increased from 1.01 billion to 1.18 billion. Engagement also increased as evidenced by the DAU-to-MAU ratio improving to 66% this year.

Facebook also provided an update on average user time spent per day across Facebook, Instagram, and Messenger. Users now spend an average of 50 minutes per day as of the company's first-quarter earnings report. That's up from the 40 minutes per day the company reported in the second quarter of 2014.

Additionally, Facebook has managed to display more advertisements in user's News Feeds and Instagram feeds. Total ad impressions increased 50% in the third quarter, in line with the first and second quarter. What's more, Facebook has managed modest average ad price increases while increasing its revenue so significantly.

Just a little bit of bad news

But a few pieces of bad news kept Facebook stock from flying too high this year. In February, India's telecom regulator banned Facebook's Free Basics app in the country, saying it violates net neutrality principles. Free Basics allowed users to access select apps (including Facebook) without the data counting against their data caps. The ban was seen as a major blow to Facebook's ambitions in the huge emerging market.

Additionally, despite reporting strong results for the third quarter, investors were scared by comments from CFO Dave Wehner saying ad load would have less of a meaningful impact on revenue growth. "With a much smaller contribution from this important factor going forward, we expect to see ad revenue growth rates come down meaningfully," Wehner said on the third-quarter earnings call.

The comments sent Facebook shares tumbling from an all-time high of $133.50 before Facebook reported its third-quarter earnings.

The Chan Zuckerberg Initiative launches

Zuckerberg has already started to make good on his plan to donate 99% of his wealth to nonprofits over his lifetime. Shareholders approved a complex 3-for-1 stock split in June, which established a new class of shares (class C) that hold no voting power. The new class of shares should enable Zuckerberg to make good on his promise without losing control of his company.

In August, Zuckerberg sold $95 million worth of stock -- about 0.2% of his net worth at the time -- to fund investments made by the Chan Zuckerberg Initiative. The CZI's first investment led the Series B funding round for Andela, an Africa-based coding bootcamp and four-year fellowship program for software engineering. It also led a $50 million round of investments for Byju, an app-centric education start-up based in India.

In September, the Chan Zuckerberg Initiative announced plans to invest at least $3 billion over the next decade toward preventing, curing, and managing all diseases by the end of the century.

Overall, it was a pretty good year for Mark Zuckerberg. He's about $6 billion richer than he was last year, and he's been able to help make the world a better place.