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Plain-language guides to your cycle, from the Lunation editorial team. Every guide gives the short answer first and lists its sources.

Topics

Menstrual cycleHow the menstrual cycle works, its phases, and what a typical cycle length looks like. 2 guides.
PeriodsPeriod length, flow, timing and the everyday questions that come with them. 1 guide.
Ovulation & fertile windowWhen ovulation happens, how the fertile window is estimated, and the signs people notice. 2 guides.
PMS & symptomsPremenstrual symptoms, cramps, mood and energy changes across the cycle.
Trying to conceiveTiming, the fertile window and what to know when you are trying to get pregnant.
PregnancyDue dates, pregnancy weeks and trimesters, and the early weeks of pregnancy.
Health data privacyWhat period tracking apps collect, who can see it, and how to keep your health data private. 1 guide.

Are Period Tracking Apps Private?Some are, some aren't. Why HIPAA usually doesn't cover period apps, what went wrong with Flo, and a checklist for judging any tracker's privacy.
How Long Is a Normal Menstrual Cycle?Most cycles last 21 to 35 days, and few are exactly 28. What large studies show about cycle length by age, how much variation is typical, and when to ask.
How to Predict Your Next PeriodA simple method to estimate your next period: average your recent cycles, add it to your last start date, and plan for a window of a few days.
What Are the Phases of the Menstrual Cycle?The four phases of the menstrual cycle explained: typical days, the hormones behind each one, and why real cycles rarely follow the 28-day textbook.
What Are the Signs of Ovulation?Stretchy cervical mucus, a positive LH test and a small rise in resting temperature are the clearest signs of ovulation. What each one tells you, and when.
When Am I Most Fertile?Your most fertile days are the six ending on ovulation day. How to find them in your own cycle, why day 14 is only a rough guide, and when to talk to a doctor.

Estimate your next period, fertile window, due date or average cycle length with the Lunation calculators.