You do NOT need to wait until you are done with your period. You can start taking the birth control pills any time.
However, we recommend starting at the end of your period because you will most likely have less spotting on your 1st pack. Also, theoretically, it’s effective immediately (if you start on your period) vs. other times, you need to use backup for 7 days.
To be absolutely safe we recommend backup or abstain for the first month. For more information, click here.