No more than 36 hours may pass between two pills, while the pill free period must never be longer than 7 days. If more than 36 hours passes in between two pills the risk of pregnancy is greatest at the start and the end of each pack. What to do if you forgot to take a pill and don’t want to run the risk of pregnancy?
Forgotten pill(s) in the first week
Forgotten pill(s) in the second week
Forgotten pill(s) in the third week

NB. For the mini-pill there are different rules!