By my math, Eduardo Saverin doesn’t avoid any tax at all by leaving the US, regardless of whether or not his stock goes up or down. If he leaves, the US takes 15% of his stock now. If he stays, the US takes 15% of his stock later. But either way, the US have taken away 15% of his ability to spend.<p>Let’s work through it with numbers, in case that isn’t clear. Say Saverin has $100 worth of Facebook stock. He renounces US citizenship. He sells enough stock to pay $15 to the government, leaving him with $85 in Facebook stock. Over the next year, Facebook doubles in value, leaving him with $170 in stock. He cashes out, and there’s no tax, so he ends up with $170 in cash.<p>Now imagine he stays in the US. He has $100 in Facebook stock, which he pays no tax on because there is no taxable event. Facebook doubles in value over the next year, so he ends up with $200 in stock. Then he cashes out, paying 15% in capital gains, leaving him with $170 cash.<p>Clearly he ends up with the same amount of cash either way. Perhaps Saverin is avoiding tax by leaving the US, but neither this article nor any other article I have read identifies how he is doing so.