<p>Facebook's IPO made founder Mark Zuckerberg a billionaire -- but left him with a tax bill likely to top $1 billion.</p><p>NEW YORK (CNNMoney)</p><p>Zuckerberg's whopping tax hit stems from his move last May to increase his stake in Facebook. On the day of Facebook's initial public offering, Zuckerberg exercised a stock option and purchased 60 million Facebook shares at a "strike price" of 6 cents each.</p><p>Even if those shares are never sold, the IRS treats them as ordinary income at the time the options are exercised. The rationale is that such options are a form of compensation, just like regular wages.</p><p><a href="http://money.cnn.com/2013/03/28/technology/zuckerberg-tax-bill/">Keep reading...</a></p><p>Read also:</p><p><a href="http://www.nydailynews.com/news/national/facebook-founder-hit-1-1-billion-tax-bill-2012-article-1.1302197">Is there a &#039;dislike&#039; button? Facebook founder Mark Zuckerberg hit with $ 1.1 ...</a> (New York Daily News)</p><p><a href="http://blogs.ajc.com/business-beat/2013/03/28/facebook-founder-zuckerberg-plans-lobbying-group/?cxntfid=blogs_business_beat">Facebook founder Zuckerberg plans lobbying group</a> (Atlanta Journal Constitution (blog))</p><p><a href="http://www.huntingtonnews.net/58824">Do you Want to Help Pay Facebook Mark Zuckerberg&#039;s Taxes?</a> (HNN Huntingtonnews.net)</p><p>Explore: <a href="http://news.google.com/news/more?ncl=d_AUzsxWKSJeSKMxrSuzvseOd-qOM&ned=us">14 additional articles.</a></p>