Good morning ladies I recently just went on birth control after having my son and it's been so long since I've actually…

Good morning ladies I recently just went on birth control after having my son and it's been so long since I've actually been on it that I'm wondering how long after starting does it take you to be safe from pregnancy is it exactly the first seven days from start to finish meaning Sunday through Saturday those 7 days can you give me some info cuz I'm unsure??