You can log menstrual cycle information to get period and fertile window predictions.
Siri: On , then tap Cycle Tracking.
Tap Get Started, then follow the onscreen instructions.
To help improve predictions for your period and fertile windows, enter the requested information.
You can log the days of a period and track information like symptoms, spotting, basal body temperature, and more.
Go to the Health app Use Cycle Tracking on Apple Watch in the Apple Watch User Guide.
Your logged information appears in the timeline at the top of the screen, where a solid red circle , then tap Cycle Tracking.
Swipe the timeline to select a day.
Tap a category of data (such as Menstruation or Symptoms), make your changes, then tap Done.
To unmark a period day, tap its solid red circle in the timeline.
When you enter information about pregnancy, lactation, and contraceptive use, that information is used to help manage your cycle predictions.
Tap View menstrual cycle predictions and history in Health on iPadApple Support article: Track your period with Cycle Tracking