If a home ovulation test says you are ovulating, is the plan b pill not likely to prevent pregnancy?

Incorrect: Plan b does not prevent ovulation. It actually works by preventing implantation of an egg onto the uterus. Keep in mind that nothing is 100% effective, and that Plan B works best if the directions are followed exactly.

It should work: The Plan B regimen is designed to prevent implantation of a fertilized ovum. If you don't ovulate you don't need it.