How accurate are period predictions?

Period prediction accuracy drops with cycle irregularity. For regular 28-day cycles, predictions are accurate ±1–2 days. Irregular cycles (PCOS, stress, perimenopause) can vary by 7+ days. Tracking actual start dates with an app improves accuracy over time. Use predictions as estimates, not guarantees.

What is a normal menstrual cycle length?

Normal cycle length: 21–35 days. Average: 28 days. Period duration: 2–7 days. Heavy days: typically days 2–3. Cycle length can vary month to month by up to 7 days and still be normal. Consistent cycles outside 21–35 days, or heavy bleeding, should be discussed with a healthcare provider.

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