Basal Body Temperature


What is the basal body temperature method?

The basal body temperature method is a technique used in family planning. Basal temperature is the temperature of your body when you are completely at rest.

After a woman ovulates (releases an egg from the ovary), her body temperature rises slightly. While tracking the basal body temperature during multiple menstrual cycles cannot actually predict when you are going to ovulate, it can help to establish a pattern. You will then be able to understand when you are likely to ovulate.

Detecting ovulation can help you identify the days you are most likely to become pregnant. With this information, you can tell the best days to have sex if you want to become pregnant. It also helps you know which days you should avoid sex or use another birth control method to avoid becoming pregnant.

Why is the basal body temperature method used?

People use this method to determine a woman’s most fertile days of the month. Some women who want to get pregnant measure basal body temperature to identify the best days of the month to have sex. Women trying to avoid pregnancy may use it to know which days they should avoid having sex.

Some women choose the basal body temperature method because they do not want to take medications or hormones for birth control. In some cases, people use the method for religious reasons.

In any case, it might take a while to get used to tracking and recording temperatures and to being aware of the changes in your body. Other signs that indicate where you are in your cycle include breast tenderness, pains near an ovary, and the state of your cervical mucus. Many women keep track of the day that their periods start and when they end.

Procedure Details

How does the basal body temperature method work?

To use the basal body temperature method:

  • Make sure you have a thermometer that measures temperatures to at least one-tenth of a degree. This could be a regular digital thermometer or a special basal body temperature thermometer.
  • Take your basal temperature at the same time every day. The best time to take this temperature is immediately after waking up. Your body usually reaches its basal temperature when you are asleep..
  • Measure the temperature from the same place every day. The basal body temperature can be taken in the mouth, vagina, or rectum.
  • Record the temperature each day. Use a graph, list, or fertility-tracking app that allows you to compare each day’s temperature.
  • Identify a temperature increase. Basal body temperature typically rises less than ½ of a degree Fahrenheit after ovulation. It may take a few cycles to determine when this rise occurs each month.
  • Consider the fertile period. You are most likely to get pregnant during the period spanning 2 days before and 3 days after ovulation. If you are hoping to become pregnant, have sex during this time. If you want to avoid pregnancy, do not have unprotected sex until the fourth day after ovulation.

Risks / Benefits

What are the benefits of the basal body temperature method?

The basal body temperature method has no side effects. The only cost is the price of the thermometer.

What are the drawbacks of the basal body temperature method?

The basal body temperature method may not accurately predict ovulation in all women, including those with irregular menstrual cycles. It offers no protection from sexually transmitted diseases.

Sometimes this method is not effective in preventing pregnancy due to outside factors that can affect basal body temperature. Factors that can alter this temperature include:

  • Breastfeeding
  • Drinking alcohol
  • Fever caused by illness or infection
  • Oversleeping
  • Stress
  • Taking some medications
  • Traveling to different time zones

When to Call the Doctor

When should I contact my doctor about the basal body temperature method?

Ask your doctor if the basal body temperature method may work for you. Many family planning experts recommend combining the basal body temperature method with other methods of natural family planning such as the cervical mucus method.

Last reviewed by a Cleveland Clinic medical professional on 04/23/2019.


  • Knowledge for Health Family Planning Handbook. Basal Body Temperature (BBT) Method. ( Accessed 4/24/2019.
  • Planned Parenthood. What’s the Temperature Method of FAMs? ( Accessed 4/24/2019.
  • American Pregnancy Association. Fertility Awareness: Natural Family Planning. ( Accessed 4/24/2019.

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