Ovulation Calculator

How ovulation timing is estimated

Ovulation is the release of an egg from the ovary, and it usually happens about 14 days before your next period starts. That gap, called the luteal phase, is fairly consistent even when cycle length varies. So this calculator estimates ovulation as last period + (cycle length − 14) days. For a typical 28-day cycle that lands on day 14, while a 32-day cycle moves it to about day 18. Your next period is estimated as simply one full cycle length after the date you entered.

Because the calculation is anchored to the first day of your last period, the most important input is an accurate start date. If your cycles vary from month to month, using an average length over several cycles gives a more representative estimate than a single month.

The fertile window

Conception is possible on more than just ovulation day. Sperm can survive in the reproductive tract for up to about five days, and the released egg remains viable for roughly 24 hours. The fertile window therefore spans the five days before ovulation through ovulation day, a span of about six days. The two to three days leading up to and including ovulation are generally the most fertile. This tool highlights that window so you can plan around it whether you are trying to conceive or simply tracking your cycle.

Limitations and a health note

Calendar estimates work best for regular cycles and are less reliable if your cycles are irregular, if you are coming off hormonal birth control, or around perimenopause. For greater accuracy, many people combine the calendar with ovulation predictor kits, basal body temperature charting or cervical mucus observations. This calculator is not a contraceptive method and should not be relied on to prevent pregnancy. It is for general information only and is not medical advice. All calculations run locally in your browser and nothing is uploaded.