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How the Ovulation Calculator Works

Based on the first day of your last period, the average number of days in your menstrual cycle, and your average luteal phase length, the ovulation calculator predicts ovulation dates and fertile days. The predicted ovulation date and fertile days in each menstrual cycle are approximate dates only; this ovulation calculator is intended for use by those with regular cycles.

The luteal phase of the menstrual cycle is the number of days between ovulation (release of an egg from the ovary) until the day before your next menstrual period starts. For many women with regular menstrual cycles, the luteal phase is generally from 10 to 16 days, with 14 days being the average length. If you know your luteal phase length (because you've either charted your fertility cycles in the past, or have used ovulation prediction kits), you can specify it in the entry field on the criteria screen; otherwise, you can leave 14 (the average) as the default luteal phase length, which is what most other ovulation calculators automatically use.

MyMonthlyCycles Luteal Phase Calculator - calculates your luteal phase length.

To calculate the approximate ovulation date for a given cycle, the calculator does the following:

  1. It calculates the first day of your next menstrual cycle. That is, the day when your next menstrual period begins. This calculation is performed by adding your cycle length to the first day of the preceding menstrual period.

    For example, if the first day of your last period was January 1, and your cycle length is 28 days, your next period would begin on or about January 29th.

  2. Next, the calculator subtracts your luteal phase length from the first day of your next period, yielding the approximate date of ovulation in the current cycle.

    Continuing the above example, if your luteal phase length is 14 days, it would subtract 14 from January 29th. The result, January 15th, is the approximate date of ovulation for the menstrual cycle that began on January 1st.

The fertile days are calculated based on the following: male sperm can live from 3 to 5 days in fertile cervical mucus. A female egg, once ovulated, can survive for up to 24 hours.

As a result, you are likely fertile a few days before ovulation, up to and including the day of ovulation, and for 12 to 24 hours thereafter, as shown on the resulting chart.

Disclaimer: The information on this ovulation calendar should not and cannot be used to reliably prevent pregnancy. This calculator is not intended for those having irregular cycles; if your cycle is irregular, talk to your healthcare provider regarding methods that can help determine your fertility cycles.

Even if your cycles are regular, we make no guarantee that your period, ovulation, and/or fertile days will occur on the predicted dates shown on the calculated ovulation calendar, since each person's menstrual and fertility cycles can vary in any given month for a variety of reasons.

All information provided on this ovulation calculator, including predicted dates of menstruation, ovulation and fertile days, is for educational purposes only. It is not intended as a substitute for advice provided by a medical doctor or qualified healthcare provider. You should not use this information for self-diagnosis or for treating a health problem or disease. If you have any questions whatsoever about your medical health or believe you have a medical problem or disease, you should contact your medical doctor or healthcare provider.