You should get your period about once every month. A typical menstrual cycle is about 28 days. This means that there should be about 28 days from the first day of your period to the first day of your next period. 28 days is an average number, but anywhere between 21 and 35 days is normal. In the first year you should have at least 4 periods, the second year at least 6 periods, and for the 3-5th year, at least 8 periods. Adults should have at least 9 periods a year. Your period will usually last between 3 and 7 days.