Understanding Your Menstrual Cycle
Phases, normal length and when to see a doctor.
Phases
The cycle has menstrual, follicular, ovulatory and luteal phases. Hormones oestrogen and progesterone rise and fall across them.
What is normal
Cycles from 21 to 35 days are typical in adults, with bleeding lasting up to seven days. Variation of up to seven days between cycles is common.
When to seek care
See a clinician for periods missing for three months, very heavy bleeding, severe pain or cycles shorter than 21 or longer than 35 days.
Try it: Menstrual Cycle Length Calculator
Example with sample values. Open the full calculator →
Average cycle28 days
Variation2 days
Next periodOct 19, 2026
Your cycles are regular, within the typical 21–35 day range with variation under 7 days.
Educational content only. This article does not replace advice from a qualified health professional. Medical disclaimer.