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Ovulation Calculator

Estimate your ovulation day and fertile window for the next 6 menstrual cycles.

Privacy: All calculations run locally in your browser. No data is sent to any server.
Tip: your entries are never placed in the page URL.
The first day of your most recent period.
Typical range: 21–35. Default is 28.
Note: This is an estimate based on average cycle patterns. It should not be used as a sole method for contraception. Consult a healthcare provider for personalized advice.
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About Ovulation

Ovulation is the release of a mature egg from the ovary. It typically happens about 14 days before the start of the next period, though this varies between individuals.

How this calculator works

The tool estimates ovulation as occurring on day (cycle length − 14) of each cycle. It then projects the fertile window (5 days before ovulation through 1 day after) for 6 consecutive cycles, along with corresponding due dates if conception occurs.

The fertile window

Sperm can survive inside the body for up to 5 days, and the egg is viable for about 12–24 hours after release. This means there's roughly a 6-day window each cycle when conception is possible. The highest probability is in the last 3 days before ovulation.

Tips for tracking

Calendar-based estimates work best for regular cycles. Other methods such as basal body temperature tracking, cervical mucus changes, and ovulation predictor kits (LH tests) can provide additional confirmation. Irregular cycles (shorter than 21 or longer than 35 days) make calendar predictions less reliable.

Important

This calculator is not a reliable method of contraception. It provides estimates based on averages. Always consult a healthcare provider for family planning advice.