Menstrual Cycle Length Calculator
Next Period Predictor
Predict next period and fertile window from cycle data
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Cycle Regularity Check
Assess cycle regularity from recent cycle lengths
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Formula
Days Until Next Period = Cycle Length - Days Since Last Period | Ovulation Day = Cycle Length - 14 | Fertile Window = Ovulation Day - 5 to Ovulation Day + 1
Frequently Asked Questions
What is a normal menstrual cycle length?
Normal cycles range from 24 to 38 days, with 28 days being the average. Cycles are measured from the first day of one period to the first day of the next. Some variation (up to 7-9 days) between cycles is normal. Consistently short (<24 days) or long (>38 days) cycles should be evaluated.
When is the fertile window in a menstrual cycle?
The fertile window spans approximately 6 days: the 5 days before ovulation and the day of ovulation itself. Ovulation typically occurs about 14 days before the next period starts. For a 28-day cycle, this means around day 14. Sperm can survive up to 5 days in the reproductive tract.
What causes irregular periods?
Common causes include stress, significant weight change, excessive exercise, PCOS, thyroid disorders, perimenopause, new birth control, breastfeeding, and certain medications. Occasional irregularity is normal. Persistent irregularity lasting 3+ months should be evaluated by a healthcare provider.
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