The menstrual cycle calculator turns one known period start date into calendar references for everyday planning: an estimated next period, an estimated ovulation date, a possible fertile window, and a day-based current-phase label. It answers “where might these dates fall under these inputs?” rather than detecting what your body has actually done.
It can help with reminders, travel planning, supply preparation, and cycle notes. The current page uses only one last-period date, an average cycle length, and a usual period length. It does not use multiple cycles of history, symptoms, basal body temperature, cervical mucus, ovulation tests, or hormone results.
For contraception, conception planning, or questions during pregnancy, postpartum, breastfeeding, perimenopause, or medication changes, treat this as supporting information and ask a clinician or qualified professional for guidance.
Enter the first day of the most recent period; the page does not allow a future date. The value is a calendar date calculated in the browser’s local date context. If the starting date is off by a few days, the entire projected timeline moves with it.
No. It uses 14 days before the predicted next period as a calendar estimate; it does not detect or prove actual ovulation.
You can use it as a rough reminder, but dates and windows become less reliable as cycle variation grows, so do not use it alone for contraception or conception.
It does not change the core date formula; it mainly affects the menstrual-phase label and cycle illustration.
Talk with a clinician about unusual pain, unusual bleeding, persistently irregular cycles, or difficulty conceiving.
Estimate the next period, ovulation date, and a possible fertile window from the last period date, average cycle length, and usual period length; calendar reference only, not medical or contraceptive advice.