The pricing policy of the low-cost carriers is usually very dynamic, with discounts and tickets in promotion. Like other carriers, even if the advertised price may be very low, it often does not include charges and taxes. With some airlines, some flights are advertised as free (plus applicable taxes, fees and charges). Depending on the airline, perhaps as many (or as few) as ten percent of the seats on any flight are offered at the lowest price and are the first to sell. The prices steadily rise thereafter to a point where they can be comparable or more expensive than a flight on a full-service carrier.