Menstrual Cycle Calculator
A menstrual cycle calculator tracks the timing of periods, ovulation, and fertile windows based on cycle length and period duration. The average cycle is 28 days (range 21–35 days), with ovulation typically occurring 14 days before the next expected period.
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Tip: Cycle tracking apps are not reliable contraception. Only fertility awareness methods (FAM) with proper education provide effective natural family planning.
- 1Next period = Last period start + Cycle length
- 2Ovulation = Next period − 14 days
- 3Fertile window = Ovulation day ± 5 days (sperm viable 5 days; egg viable 12–24 hours)
- 4Luteal phase (ovulation to next period) is relatively fixed at ~14 days
28-day cycle, last period 1 Jan=Next period: 29 Jan · Ovulation: ~15 Jan · Fertile window: 10–16 JanStandard cycle
35-day cycle, last period 1 Jan=Next period: 5 Feb · Ovulation: ~22 JanLonger cycle shifts ovulation later
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