Period Tracker / Calculator
Predict your next 3 periods based on average cycle length and recent start date.
Inputs
Next period expected
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Expected duration
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Period after that
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3rd upcoming period
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Current cycle day
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About Period Tracker / Calculator
Normal cycle range
Cycles between 21 and 35 days are considered normal in adults. Teen cycles can be 21-45 days. Cycles shorter than 21 or longer than 40 warrant a doctor visit.
Why cycles vary
Stress, weight changes, exercise intensity, sleep, illness, medication, and approaching menopause all affect cycles. The follicular phase (before ovulation) varies most; the luteal phase is fairly fixed at 12-14 days.
Tracking tools
Period tracking apps (Clue, Flo, Apple Health) detect patterns over months and predict more accurately than averaging. Bodily symptoms (cramping, mood, discharge) also help.