Birth control pills are efficient (>99% of the time) only if they are taken regularly! This means that you must take one pill every day for at least 21 days. The last 7 pills (from day 22 to day 28) are inactive pills (don’t contain hormones) and you should get your period while taking them. Some types of birth control pills packs don’t even contain 28 pills but only 21. In those cases, a pause of 7 days is made before starting a new pack.