WhatsApp's cofounder could be leaving $1 billion on the table by quitting Facebook

Reuters

• WhatsApp cofounder Jan Koum is leaving Facebook, which acquired his company in 2014 for $19 billion.
• Koum is leaving before his stock award fully vests. He could be losing as much as $1 billion in Facebook stock.
• He's sold over $7 billion in Facebook stock so far.

WhatsApp cofounder Jan Koum announced on Monday that he plans to resign from Facebook, which means he might be leaving a lot of money on the table.

Depending on when Koum's last day at Facebook is, he might lose out on as much as $1 billion in stock awards, Bloomberg reported, citing public filings.

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Facebook bought WhatsApp in 2014 for $19 billion, making Koum and his cofounder Brian Acton billionaires. Both have now left Facebook before the traditional four-year cliff.

Usually, stock awards after a merger are distributed on a four-year "vesting cliff." If you last all four years, you get your entire stock grant.

Koum still has three vesting dates through the end of 2018 - one in May, one in August, and the final one in November, according to Bloomberg. The value of the shares he would get if he still worked at Facebook is just under $1 billion at the current Facebook share price.

Koum will also leave Facebook's board of directors, the company confirmed in an SEC filing.

Don't cry for Koum, though. He's already sold about $7.1 billion worth of Facebook shares, according to Courtney Yu, director of research at Equilar, which tracks board compensation. He still holds over 11 million shares of Facebook, worth over $2 billion at current market value.

So he's got plenty of money, even if he is leaving stock on the table. In his goodbye note, said he planned to collect "rare air-cooled Porsches."

Here's the goodbye note Koum posted to Facebook:

It's been almost a decade since Brian and I started WhatsApp, and it's been an amazing journey with some of the best people. But it is time for me to move on. I've been blessed to work with such an incredibly small team and see how a crazy amount of focus can produce an app used by so many people all over the world.

I'm leaving at a time when people are using WhatsApp in more ways than I could have imagined. The team is stronger than ever and it'll continue to do amazing things. I'm taking some time off to do things I enjoy outside of technology, such as collecting rare air-cooled Porsches, working on my cars and playing ultimate frisbee. And I'll still be cheering WhatsApp on - just from the outside. Thanks to everyone who has made this journey possible.

Rob Price and Matt Weinberger contributed reporting.