Teaching time is defined as the net contact hours of teaching. It is calculated on the basis of the annual number of weeks of instruction multiplied by the minimum/maximum number of periods, which a teacher is supposed to spend teaching a class or a group, multiplied by the length of a period in minutes and divided by 60. Periods of time formally allowed for breaks between lessons or groups of lessons, and days when schools are closed for public holidays and festivities, are excluded. In primary education, however, short breaks that teachers spend with the class are typically included.