Think of an ETF as a mutual fund that trades like a stock. Just like an index fund, an ETF represents a basket of stocks that reflect an index such as the S&P 500. An ETF, however, isn’t a mutual fund; it trades just like any other company on a stock exchange. Unlike a mutual fund that has its net-asset value (NAV) calculated at the end of each trading day, an ETF’s price changes throughout the day, fluctuating with supply and demand. It is important to remember that while ETFs attempt to replicate the return on indexes, there is no guarantee that they will do so exactly. It is not uncommon to see a 1% or more difference between the actual index’s year-end return and that of an ETF.