Your Cycle: A User's Guide

Whether we like it or loathe it, our hormones wield a lot of power over our bodies. They can make you feel calm and more confident or edgy and self-doubting, and that affects how you handle any situation—whether you freak out when your boss gives you a last-minute project, for instance, or whether you find the willpower to resist that second piece of chocolate cake. "The ups and downs of estrogen, progesterone and testosterone influence your behavior throughout the month," explains Scott Haltzman, clinical assistant professor of psychiatry and human behavior at Brown University in Providence, Rhode Island.

Because so many of us are confused about how our hormones affect us on a daily basis, we asked top experts to demystify these fluctuations—and explain how you can use hormonal shifts to your advantage.

Certain hormones set our minds and bodies up for success at different types of activites. In a nutshell, keep this in mind:

Days 1 to 9: Get a mammogram
Days 1 to 14: Quit smoking
Days 3 to 10: Attack a stressful problem; take a risk
Days 3 to 25: Start a diet
Days 6 to 11: Go to the dentist
Days 10 to 13: Make a baby; ask for a raise
Days 10 to 20: Get a Pap test
Day 13: Have great sex
Days 15 to 28: Burn more fat
Days 24 to 28: Make a major decision (watch out for PMS, though)

For the full details, see the slideshow Best Days of Your Cycle For…