The menstrual cycle has four phases. Here is a citable reference of each phase, its typical day range in a 28-day cycle, the main hormones and what happens.
⬇ Download JSON dataset| Phase | Typical days | Main hormones | What happens |
|---|---|---|---|
| Menstrual | 1–5 | Oestrogen & progesterone lowest | The uterine lining (endometrium) sheds — this is the period. Day 1 is the first day of bleeding. |
| Follicular | 1–13 | FSH then rising oestrogen | The pituitary releases FSH; follicles develop in the ovary and one matures, while oestrogen rebuilds the lining. Overlaps with the menstrual phase. |
| Ovulation | ~14 | LH surge, oestrogen peaks | A surge of luteinising hormone (LH) releases the mature egg. The fertile window spans roughly the few days before and the day of ovulation. |
| Luteal | 15–28 | Progesterone rises | The empty follicle becomes the corpus luteum and secretes progesterone, thickening the lining. If no pregnancy occurs, hormones fall and the next period begins (PMS may appear). |
General educational information based on a textbook 28-day cycle. Real cycles vary widely in length and timing between people and from month to month; day ranges here are averages, not predictions. This is not medical advice — for health concerns consult a qualified healthcare professional.
Everyone’s cycle is different, so the most useful data is your own. Cyca tracks your period, phases and best days entirely on your phone — no account, no ads and nothing sent to a cloud. Check the App Store listing for current access details in your region.
Get Cyca on the App Store →Free to reuse under CC BY 4.0 — attribution (a link back to this page) is all that is required. Copy the citation below:
Lumi Apps (2026-07-10). The 4 phases of the menstrual cycle. CC BY 4.0. https://alice51849.github.io/ios-app-guide/data/menstrual-cycle-phases.html
Data licensed under CC BY 4.0. You may reuse it freely — please credit “Lumi Apps (https://alice51849.github.io/ios-app-guide)”. Machine-readable copy: menstrual-cycle-phases.json.