Home > Health Library > Basal Body Temperature (BBT) Charting
The basal body temperature (BBT) is a person's at-rest
temperature. Women can track their BBT to find out when they are
ovulating. With this time line, a woman can learn when
she is most and least likely to become pregnant.
When are you most likely to become pregnant?
weeks before your period you will
ovulate, which means that one of your ovaries has released
an egg. You are most likely to get pregnant on the day of ovulation and the
5 days before it.
When are you least likely to become pregnant?
Your egg is fertile for about 12 to 24
hours after you ovulate. Avoiding sex until several days after ovulation may
help you prevent pregnancy. Keep in mind that your cycle can change, making it
hard to know when you are ovulating. Some women use this information as a form
of birth control. But it isn't very reliable for preventing pregnancy.
How can you predict when you will ovulate?
Your body temperature dips a bit just before your ovary releases an egg.
Then, 24 hours after the egg's release, your temperature rises and stays up for
several days. Before ovulation, a woman's BBT averages between
97°F (36.1°C) and
97.5°F (36.4°C). After
ovulation, it rises to
97.6°F (36.4°C) to
You can track your cycle by taking your BBT every morning. Take your
temperature at the same time every day before getting out of bed. Next, record
the results on a chart. If you have a somewhat regular cycle, the chart will
help you predict when you will ovulate next.
What tools do you need to take your basal body temperature?
The change in
your body temperature is very slight, so you need to use a special thermometer.
You can use a regular digital thermometer or buy a basal thermometer. A basal
thermometer shows you the temperature in tenths of a degree. This allows you to
note tiny changes in body heat. This thermometer is faster and more exact than
a regular thermometer.
Use a simple
Fahrenheit temperature chartFahrenheit temperature chart(What is a PDF document?) or Celsius temperature chartCelsius temperature chart(What is a PDF document?) to track your temperature for several months.
Where can you get a basal thermometer?
You can find a basal thermometer or
digital thermometer in a pharmacy or in the pharmacy section in many grocery
stores. You can also find kits that include materials for measuring and
charting BBT. These items are low in cost.
Current as of:
June 4, 2014
Kathleen Romito, MD - Family Medicine & Femi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology
How this information was developed to help you make better health decisions.
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