How the Period Calculator Works
The calculator adds your cycle length to your last period start date to predict the next period. Ovulation is estimated at cycle length minus 14 days (the luteal phase is typically 14 days in most cycles). The fertile window spans 5 days before ovulation through ovulation day.
Frequently Asked Questions
What is a normal menstrual cycle length?
A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the average. Cycle length is counted from the first day of one period to the first day of the next. Cycles can vary from month to month and this is considered normal.
When is the fertile window in a menstrual cycle?
The fertile window is typically the 5 days before ovulation plus the day of ovulation itself. In a 28-day cycle, ovulation usually occurs around day 14. Sperm can survive up to 5 days in the reproductive tract, so the fertile window spans roughly days 10â15.
What can cause an irregular menstrual cycle?
Common causes of irregular cycles include stress, significant weight changes, intense exercise, polycystic ovary syndrome (PCOS), thyroid disorders, perimenopause, and certain medications. If your cycles are consistently irregular or very painful, consult a healthcare provider.
This calculator provides estimates based on average cycle patterns and is not a substitute for medical advice. Do not use period predictions for contraception. Consult a healthcare provider for fertility planning or if you experience irregular cycles.