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Why buying an inverse ETF does not give same results as shorting the ETF
Suppose that the ETF is currently at a price of $100.  Suppose that the next day it moves up 10% (to a price of $110) and the following day it moves down 5% (to a price of $104.5).  Over these two days the ETF has had a net gain of 4.5% from its original price. The inverse ETF reverses the daily gains/losses of the base ETF.  Suppose for simplicity that the inverse ETF also starts out at a price of $100.  So on the first day it goes down 10% (to $90) and on the second day it goes up 5% (to $94.5).  Thus over the two days the inverse ETF has had a net loss of 5.5%. The specific dollar amounts do not matter here.  The result is that the ETF winds up at 110%*95% = 104.5% of its original price and the inverse ETF is at 90%*105% = 94.5% of its original price.  A similar example is given here. As suggested by your quote, this is due to compounding.  A gain of X% followed by a loss of Y% (compounded on the gain) is not in general the same as a loss of X% followed by a gain of Y% (compounded on the loss).  Or, more simply put, if something loses 10% of its value and then gains 10% of its new value, it will not return to its original value, because the 10% it gained was 10% of its decreased value, so it's not enough to bring it all the way back up.  Likewise if it gains 10% and then loses 10%, it will go slightly below its original value (since it lost 10% of its newly increased value).