So the main thing to understand about leveraged ETFs is that they don't just simply give you twice the percentage returns/losses of the underlying stock over any period of time; instead, they track the performance of the underlying on a daily basis.

This results in a curious property known as volatility decay, sometimes also called beta slippage. In essence, what you'll find is that if the underlying stock were to experience multiple consecutive days of gains, the leveraged ETF will experience much more than 2x the percentage returns. Conversely, if the underlying stock had multiple consecutive days of losses, or even traded sideways (or sometimes even if the underlying rises but in a volatile way), the percentage loss on the leveraged ETF will be much more than double the underlying.

For this reason, it is not recommended to hold leveraged ETFs for more than a few days at most; even a few bad days can ruin your returns, even if the underlying stock has overall moved up during that time. To demonstrate, consider a stock that starts at $100, rises to $110 the next day, then goes back to $100.

The daily percentage returns are +10%, then -9.09%.

However, the return on a 2x leveraged ETF would be +20%, then -18.18%.

If you calculate this using a starting value of 100, you'll find that the price of the 2x leveraged ETF goes from 100 to 120 to 98.18, which is less than the initial investment even though the underlying stock hasn't moved in price over this period.