The students of lower grades than the ones in the table can also compete if they feel prepared for the level. The age limit for the Olympiad is 19 or as long as the students are in high school.
Little Hippo category students compete in the regular category independent of the type of school they come from.
Special categories are aimed at students who are considered bilingual according to the Hippo Olympiad regulations as well as for the international schools and the schools where the majority or all subjects are taught in English (except for the countries where English is the only official language, e.g. UK). These students can compete in one of the following two categories: