Ovulation Calculator
Enter the first day of your last period and your usual cycle length. The calculator estimates when you are likely to ovulate, your fertile window, and the same dates for the next six cycles.
Type a number and the answer appears straight away.
The math behind it: Ovulation
ovulation = first day of last period + (cycle length - 14) days
Ovulation usually happens about 14 days before the next period starts. In a 28-day cycle that is day 14; in a 32-day cycle it is day 18. The fertile window covers the five days before ovulation and the day after, because sperm can survive for several days.
This is an estimate based on averages, and general information, not medical advice. Cycles vary from month to month, so do not rely on these dates to avoid pregnancy.
Common questions
How do I calculate my ovulation day?
Subtract 14 from your cycle length and count that many days from the first day of your last period. With a 30-day cycle, ovulation is around day 16.
How many days after my period do I ovulate?
In a 28-day cycle with a 5-day period, ovulation comes about 9 days after the period ends, on day 14. Longer cycles ovulate later and shorter cycles earlier.
How long does the fertile window last?
About six or seven days: the five days before ovulation, the day of ovulation and roughly a day after. The two days before ovulation and the day itself are the most fertile.
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