Cycle basics
How cycles work, what is normal, and how predictions are made.
Cycle basics
How do period trackers predict your next period?
Most period trackers predict your next period by averaging the length of your recent cycles and counting forward from the first day of your last period.
Read the guide: How do period trackers predict your next period?
Cycle basics
What is a normal menstrual cycle length?
For adults, a normal menstrual cycle is about 21 to 38 days long, counted from the first day of one period to the first day of the next.
Fertility
What is the fertile window, and how do BBT and LH tests help find it?
Your fertile window is the six days that end on the day you ovulate.
Read the guide: What is the fertile window, and how do BBT and LH tests help find it?
Conditions and life stages
Tracking for PCOS, PMDD, endometriosis and perimenopause.
Conditions
How do you track PMDD symptoms?
Rate each symptom once a day on the same simple scale, mark the days you bleed, and keep going for at least two menstrual cycles.
Conditions
How do you track your cycle with PCOS?
Log the first day of every period, how long you bleed, and symptoms such as acne, extra facial or body hair, and mood, and keep logging when months pass without a period.
Life stages
What should you track during perimenopause?
Track the start date and flow of each period, plus hot flashes, night sweats, sleep and mood.
Conditions
How do you track endometriosis pain?
Each day, rate your pain from 0 to 10, note where it is and what it feels like, and mark your period days.
Privacy
What to check before you trust an app with your cycle data.
Privacy
Is your period tracker data private?
It depends on the app. In the US, HIPAA generally does not protect health information you enter into a consumer app for your own use, so your privacy rests on each app's practices and promises.
How we write these guides
We use primary sources such as WHO, ACOG, NIH, CDC, NICE and peer-reviewed studies, and we show when each guide was published and last updated. The guides have not yet been reviewed by a clinician. Read our editorial policy.