Mark Zuckerberg Will Give Away More Than You Think by Dan Primack @FortuneMagazine December 4, 2015, 3:07 PM EDT E-mail Tweet Facebook Linkedin Share icons Ever since Mark Zuckerberg announced on Tuesday that he and wife Priscilla Chan will give away 99% of their Facebook shares, there has been all types of analysis and commentary. A lot of it has been laudatory. Some has been critical, with particular emphasis on how the “Chan Zuckerberg Initiative” will be structured in a way that could reduce the couple’s tax bill (something Zuckerberg yesterday fought back against). But almost every story and blog post used the same dollar figure for what that 99% equaled: $45 billion. It’s almost certainly wrong. To be fair, that’s the number Zuckerberg included in his original announcement. But he also qualified it with the word “currently.” As in, those Facebook FB shares were worth around $45 billion at the time of his blog post. As of last check, Zuckerberg holds 426,252,091 of Facebook stock. At market open on Tuesday, they were worth $44.68 billion. At market close that very same day, they were valued nearly $1 billion higher. One year earlier, they were valued just below $32.9 billion. Two years earlier they were worth $20 billion. Zuckerberg is just 31 years old. Chan is 30. The plan to to donate/invest/etc. the shares over the course of their lifetimes — which should mean at least 40 more years. Just assuming very modest stock price appreciation, the $45 billion figure would be the low-water mark. Moreover, the plan is to recommit any investment proceeds, thus only further expanding the pot. So feel free to think whatever positive or negative thoughts you want about the Chan Zuckerberg Initiative. But don’t think that it’s only worth $45 billion.