Ov

Ovulation Calculator

Your likely ovulation day and fertile window from your last period and cycle length.

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Result…

days

From the first day of one period to the first day of the next.

days

Days from ovulation to the next period; 14 if you don't know.

 

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How it's calculated

Ovulation ≈ first day of last period + cycle length − 14 (the luteal phase)
Fertile window = the 5 days before ovulation + ovulation day
Next period = last period + cycle length

The phase after ovulation is fairly steady at about 14 days, so ovulation is counted back from the next expected period, not forward from the last. Sperm can survive up to five days, which makes the fertile window six days long. Cycles shift from month to month; ovulation test kits or temperature charting pin it down better. Never rely on a calendar method for contraception.

Your numbers, step by step

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