When should you start the birth control pill if your period ends before Sunday?

You can start the Birth Control pill at any time in your cycle. If you are set on starting on a Sunday, then you'll need to use a back up method of birth control for a week, unless it's been five days or fewer since you started your period.

Traditionally, women in the US started the birth control pill on Sunday. This has an obvious disadvantage - your health care provider's office is closed on Sunday, and many women start their pill late when they notice too late that they're out of pills. Do yourself a favor and consider starting on a weekday, as they do in most other countries.