Ovulation Window Estimator

Estimate your fertile window and ovulation day from last period date and cycle length.

First day of last period

Cycle length (days)

Enter your details above.

Rough estimate only — not for contraception. Not medical advice.

How to use

Enter last period date and average cycle length for your fertile window.

How is ovulation estimated?

Ovulation typically occurs ~14 days before the next period. The fertile window covers the 5 days before plus ovulation day.

Is this reliable for family planning?

It is a rough estimate — cycles vary. Do not use for contraception. Not medical advice; see a doctor.

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