2015 was not kind to Bill Ackman, who after being up as much as 11% though early August, saw all his paper profits vanish and then some, closing the year down 20.5%, his worst year since 2008.
Alas, 2016 is not starting any better, and this time the billionaire investor can no longer blame an "out of left field" plunge in Valeant (a name in which he dumped 5 million shares in the last week of 2015 for "tax purposes"): this time it is everything, and the bottom line is that in the first 12 calendar days of 2016, Pershing Square is down a whopping -11.4%. Actually, just make that -14% after today's rout.
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This means that about a third of the value/AUM of Pershing Square has been wiped out since August 4.
Source [4]