In the northern hemisphere, most racehorses are born between January and May. They all grow a year older on January 1, no matter their date of birth. The age and type of race they are allowed to enter are described in the Racing Code. Horses bred to race on flat ground cannot start until the beginning of their second year's flat racing season. On the other hand, horses bred for steeplechase cannot start until February 15 of their third year in hurdles and July in steeplechase. Many horses are, therefore, more than three years old when they first race.