The key factor in being able to offer low fares is to have low operating costs. However, the low cost carriers fare setting is counter to the traditional model. Low cost strategies modify the selling price of each flight as a function of the departure date. If a price is too low, the flight will fill up early and higher-yielding late-booking business will be turned away. On the contrary, if the price is too high, the flight is at risk of departing with empty seats.