Quote from NERVESASTEEL:
Okay, let�s be a little more specific about how a leveraged ETF works. In order to deliver the 2x results that the fund�s investors expect, fund management has to hold equal proportions of debt and equity at all times.
In other words, if there�s $100m invested in the fund, it has to borrow an additional $100m and make a $200m investment in the underlying index. That�s the only way that the fund can provide 2x the underlying daily return of the index.
Of course the fund doesn�t go to the local bank and borrow money every day and then invest it. It uses financial derivatives, such as swaps, options, and futures. But the overall effect is the same.
However, every day the market moves and the assets in the fund either increase or decrease in value, throwing off the leverage ratio because total assets are no longer equal to total debt. By the end of the market day, the fund�s leverage is either too high, or too low, and some kind of corrective action is required to bring it back to 2x.
In order to maintain the target leverage ratio, our fund has to buy or sell millions of dollars worth of shares every day. Not only does this increase expenses, transaction costs, and short-term capital gains taxes, but it�s also just a bad investment strategy.
Whenever the market makes a big move downward, the fund sells shares and reduces its debt level in order to maintain its target leverage ratio. This locks in losses and reduces the afund�s sset base, making it much harder to recover gains in the next market upturn.
Note that this situation is called the Constant Leverage Trap and is a well-known problem in financial modeling. Investment portfolios that try to maintain constant levels of leverage over time perform very poorly in bad market conditions because they sell off large percentages of their assets. It�s similar to a margin maintenance call.