Period & Ovulation Calculator
Calculate your ovulation day, fertile window and next six periods from your last period and cycle length.
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6-Cycle Calendar
How Are Period and Ovulation Dates Calculated?
Each new cycle starts one cycle-length after the previous period's first day, and ovulation typically occurs about 14 days before the next period — around day 14 of a 28-day cycle, day 18 of a 32-day cycle. Sperm survive up to five days, so the fertile window spans roughly the five days before ovulation plus the day itself. Enter your last period's first day, cycle length and period duration: the tool shows your estimated ovulation day, fertile window and next period, plus a six-cycle calendar with each period's dates and ovulation day.
Real cycles naturally shift a few days with stress, travel and illness, so treat the dates as estimates. This calendar method is not a reliable contraception method, and this tool is not medical advice — consult a doctor for persistent irregularity.
Frequently Asked Questions
How accurate are the predicted dates?
They assume your average cycle repeats exactly. A ±2-3 day variation is completely normal; ovulation test kits and basal temperature tracking are more precise than any calendar.
What counts as day 1 of the cycle?
The first day of actual bleeding (not spotting). Cycle length is measured from one day 1 to the next day 1.
Can I use this to avoid pregnancy?
No. The calendar method has a high failure rate because cycles vary and sperm survive for days. Consult a healthcare professional about reliable contraception.
When should I see a doctor?
If cycles are consistently shorter than 21 or longer than 35 days, bleeding lasts more than 7 days, or a period is more than a week late with no explanation.
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Period & Ovulation Calculator