How do menstrual calculators work?
Glad you asked. Basically, your body runs on a four-part “menstrual cycle” — and while you might assume that phrase means just the week of bleeding, in actuality, your menstrual cycle also refers to the weeks you don’t bleed.
You start with the menstrual cycle (your period, when the lining of your uterus sheds), followed by the follicular phase (when the follicles in your ovaries mature and get ready for the prime time: ovulation), then comes ovulation (when the egg is released), followed finally by the luteal phase (when the egg makes its way down your fallopian tubes and gets ready to bleed). Knowing this, you can track your period and your cycle.