Ovulation Date Calculator

How to use this ovulation calendar (calculator) tool

  • Pick a date on the calendar that matches the day you started your last period
  • The calendar will display your estimated ovulation date, marking it in red.
  • The days leading up to your ovulation date will appear marked in purple; those are the days you are likely the most fertile.
  • If you have records of how long your own menstrual cycle lasts, change the default number of 28 days in the dropdown menu in the results box for a more accurate calculation.

What is the best way to determine when you’re most fertile?

Being aware of your menstrual cycle and the changes in your body that happen during this time can help you know when you are most likely to get pregnant.

The average menstrual cycle lasts 28 days. But normal cycles can vary from 21 to 35 days. The amount of time before ovulation occurs is different in every woman and even can be different from month to month in the same woman, varying from 13 to 20 days long. Learning about this part of the cycle is important because it is when ovulation and pregnancy can occur. After ovulation, every woman (unless she has a health problem that affects her periods or becomes pregnant) will have a period within 14 to 16 days.

Knowing when you're most fertile will help you plan or prevent pregnancy. There are three ways you can keep track of your fertile times:

  1. calendar method;
  2. basal body temperature method; and
  3. ovulation method (cervical mucus method).

What is the calendar method of determining fertility?

Our tool above is a simplified and automated version of the calendar method of determining fertility.

To get an even more accurate idea of when you, personally, are most fertile, you can record your menstrual cycle on a calendar for eight to 12 months. The first day of your period is Day 1. Circle Day 1 on the calendar. The length of your cycle may vary from month to month. So write down the total number of days it lasts each time. Using this record, you can find the days you are most fertile in the months ahead:

To find out the first day when you are most fertile, subtract 18 from the total number of days in your shortest cycle. Take this new number and count ahead that many days from the first day of your next period. Draw an X through this date on your calendar. The X marks the first day you're likely to be fertile. To find out the last day when you are most fertile, subtract 11 from the total number of days in your longest cycle. Take this new number and count ahead that many days from the first day of your next period. Draw an X through this date on your calendar. The time between the two Xs is your most fertile window.

This method always should be used along with other fertility awareness methods, especially if your cycles are not always the same length.

What is the basal body temperature method of determining fertility?

Basal body temperature is your temperature at rest as soon as you awake in the morning. A woman's basal body temperature rises slightly with ovulation. So by recording this temperature daily for several months, you'll be able to predict your most fertile days.

Basal body temperature differs slightly from woman to woman. Anywhere from 96 to 98 degrees Fahrenheit orally is average before ovulation. After ovulation most women have an oral temperature between 97 and 99 degrees Fahrenheit. The rise in temperature can be a sudden jump or a gradual climb over a few days.

Usually a woman's basal body temperature rises by only 0.4 to 0.8 degrees Fahrenheit. To detect this tiny change, women must use a basal body thermometer. These thermometers are very sensitive. Most pharmacies sell them for about $10.

The rise in temperature doesn't show exactly when the egg is released. But almost all women have ovulated within three days after their temperatures spike. Body temperature stays at the higher level until your period starts.

You are most fertile and most likely to get pregnant:

Two to three days before your temperature hits the highest point (ovulation) 12 to 24 hours after ovulation

A man's sperm can live for up to three days in a woman's body. The sperm can fertilize an egg at any point during that time. So if you have unprotected sex a few days before ovulation, you could get pregnant.

Many things can affect basal body temperature. For your chart to be useful, make sure to take your temperature every morning at about the same time. Things that can alter your temperature include:

  • Drinking alcohol the night before
  • Smoking cigarettes the night before
  • Getting a poor night's sleep
  • Having a fever
  • Doing anything in the morning before you take your temperature - including going to the bathroom and talking on the phone

What is the cervical mucus method of determining fertility?

The cervical mucus method (also known as the ovulation method) involves being aware of the changes in your cervical mucus throughout the month. The hormones that control the menstrual cycle also change the kind and amount of mucus you have before and during ovulation.

Right after your period, there are usually a few days when there is no mucus present or "dry days." As the egg starts to mature, mucus increases in the vagina, appears at the vaginal opening, and is white or yellow and cloudy and sticky. The greatest amount of mucus appears just before ovulation. During these "wet days" it becomes clear and slippery, like raw egg whites. Sometimes it can be stretched apart.

This is when you are most fertile. About four days after the wet days begin the mucus changes again. There will be much less and it becomes sticky and cloudy. You might have a few more dry days before your period returns. Describe changes in your mucus on a calendar. Label the days, "Sticky," "Dry," or "Wet." You are most fertile at the first sign of wetness after your period or a day or two before wetness begins.

The cervical mucus method is less reliable for some women. Women who are breastfeeding, taking hormonal birth control (like the pill), using feminine hygiene products, have vaginitis or sexually transmitted infections (STIs or STDs), or have had surgery on the cervix should not rely on this method.

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Reviewed on 10/9/2019
References
Office on Women's Health, U.S. Department of Health and Human Services. "Trying to conceive." Updated: Feb 01, 2017.
<https://www.womenshealth.gov/pregnancy/you-get-pregnant/trying-conceive>