confrontNeed to stand up to a colleague who’s been pressuring you to do her work for her? Tell a cheap friend you’re no longer going to pick up the whole tab every time you hang out together? Make it clear to your roommate that your cupcakes are not community property? Or been meaning to confront someone for another reason?

Confront whoever needs confronting during Week 2 of your cycle–which is the week leading up to and including ovulation.

New research in the journal Psychoneuroendocrinology reveals that your assertiveness naturally peaks on these days due to high estrogen and low progesterone, which triggers a higher output of brain chemicals that pump up your confidence and resolve.

The study authors theorize this spike in assertiveness is timed to coincide with ovulation because it helps you become pickier about which potential mate you choose during this fertile phase. The more assertive you are when choosing a mate, the more likely you are to select someone with healthy genes.

It just so happens that this assertiveness spills over into other areas of your life, too, making it a tad easier to stand up for yourself in other types of situations.