Fertility and Your Menstrual Cycle

Knowing your menstrual cycle can help you increase your chances of becoming pregnant.

Understanding Your Menstrual Cycle

On average, a woman’s menstrual cycle is 28 days long. This can vary though, from 17 to 36 days. Cycle steps include:

  • Day 1 of your menstrual cycle begins on the first day of your period.
  • Between day 7 and 11, the lining of your uterus begins to thicken. This allows fertilized eggs to implant into it.
  • Around day 14, an ovary releases a mature egg. This is known as ovulation. The egg travels down a fallopian tube. The release timing will vary based on overall cycle length.

Sperm will fertilize the egg in the fallopian tube. The fertilized egg will then travel toward the uterus where it will implant. If this happens and the egg attaches to the lining of the uterus, pregnancy occurs.

When trying to get pregnant, it is helpful to know when the egg is released. That is the best time to become pregnant. The table below describes 4 of the most common methods that can be used to track when you are most fertile each month.

Method Description
Basal body temperature This method is best used to track your ovulation pattern over the course of a few months. It can help you begin to learn how to predict when you will ovulate. Your body temperature is lower (96-98ºF or 35.5-36.6°C) until ovulation (egg release). On the day of ovulation, your temperature will rise between 0.4 and 0.8ºF. It will stay at that level until your period starts. Take your basal body temperature (BBT) each morning at the same time before you get out of bed. Ovulation is likely when temperature stays at this higher level (97-99ºF or 36.1-37.2°C) for 3 days. Record it on a http://www.womenshealth.gov/. This will help to show ovulation. Your most fertile days are the 2 to 3 days before your temperature hits its highest point, and the 12 to 24 hours after you have ovulated. You will need to purchase a BBT thermometer at a drug store. The thermometer must be accurate enough to detect temperature changes of at least 1/10 of a degree.
Calendar You will use a calendar to track your menstrual cycle for 8 to 12 months. Circle the first day of your period on the calendar each month. Write down the length of each cycle, day 1 through the day before your next period.
  • To find the first day when you are the most fertile, subtract 18 from your shortest cycle. Mark an X on your calendar on this day of each cycle. For example, if your shortest cycle was 27 days, the first day you are the most fertile will be Day 9 of your cycle; 27-18=9.
  • To find the last day you are fertile, subtract 11 from your longest cycle and draw an X through this date. For example, if your longest cycle was 29 days, the last day you are fertile will be Day 18 of your cycle; 29-11=18.
This method cannot pinpoint the exact day you ovulate. It should be used with other methods for best effect.
Cervical mucusYou will track changes in the fluid at the opening of your cervix during your cycle. Right after your period, there will be a few days of little or no mucus, known as dry days. As the egg starts to mature, the quantity of mucus increases. It is usually white or yellow and cloudy and sticky. Just before ovulation, the greatest amount of mucus appears. It will be clear, slippery, and sometimes stretchy, similar to raw egg whites. Your most fertile days are just before and just after ovulation.
Ovulation predictor kit There are many ovulation prediction kits available in drug stores. These kits measure the amount of luteinizing hormone (LH) in your urine. They use this information to determine when you ovulate. There are 2 types of kits:
  • One type is used to measure LH for the days during your menstrual cycle you are most likely to be fertile (see the calendar method above). These kits are inexpensive.
  • A second type measures your LH level every day. It tells you when your fertility is low, high, and peak. These testing machines are more expensive.


Trying to conceive. Office on Women's Health website. Available at: https://www.womenshealth.gov/pregnancy/you-get-pregnant/trying-conceive. Accessed January 29, 2021.
Understanding ovulation. American Pregnancy Association website. Available at:
...(Click grey area to select URL)
Accessed January 29, 2021.


Office on Women's Health
The American Congress of Obstetricians and Gynecologists


The Society of Obstetricians and Gynaecologists of Canada
Women's Health Matters
Last reviewed January 2021 by EBSCO Medical Review Board
Last Updated: 1/29/2021

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