Period Calculator
Forecast upcoming menstrual cycle dates and track average period frequency.
Upcoming Cycles
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Medical disclaimer. This calculator is for general information and education only. It is not medical advice, not a diagnosis, and not a substitute for professional care. Predictions assume a regular pattern and cannot account for illness, stress, medication, contraception or perimenopause. Persistent irregularity is worth raising with a clinician.Speak to a doctor or another qualified clinician about any health decision.Last reviewed .
Frequently asked questions
How long is a normal menstrual cycle?
A normal menstrual cycle typically ranges between 21 and 35 days, with an average of 28 days.
What is a normal menstrual cycle length?
Typically 21 to 35 days in adults, counted from the first day of one period to the day before the next. Cycles in the first years after menarche and in the years approaching menopause are commonly longer and more variable. Variation of a few days month to month is normal.
Why is my period late or irregular?
Common causes include stress, significant weight change, intense exercise, travel and illness, along with medical causes such as polycystic ovary syndrome, thyroid disorders and hyperprolactinaemia. Hormonal contraception changes bleeding patterns by design. Persistent irregularity, very heavy bleeding or missed periods without an obvious cause are worth discussing with a clinician.
How accurate is period prediction?
Predictions extrapolate from your average cycle length, so they are only as regular as your cycles are. A cycle that varies by more than about seven days between its shortest and longest is considered irregular and will not predict well. Logging several cycles improves the estimate more than any single adjustment.