How soon after your period can you start the pill if your period ended on Tuesday?

You will lose protection if you start the new pack a day late. If you do that, you must use a back up method for the first seven days of that new pack. A better way to switch from a Saturday to a Sunday start is to take the first placebo pill in the pack as scheduled on Saturday, then start your new pack the next day. Doing so will not affect protection. Just remember that if you're starting the new pack on Sunday, then you may not have access to your health care provider or pharmacy on your start day; if you run out of pills, you may not be able to reach anyone at the office until Monday, and will lose protection.