How to Take Your Basal Body Temperature

Medically reviewed by Lacy Windham, MD

Last Updated: August 31, 2022 References Approved

Your basal body temperature (BBT) is your temperature when your body is at rest. Women can track their BBT to determine when they are ovulating and when they are most fertile. Taking your basal body temperature is a pretty straightforward process. Once you have your BBT, you can chart it on a graph to help you determine when you are most fertile. You can use this information to help you get pregnant or to avoid getting pregnant.

Part 1

Part 1 of 2:

Taking Your Basal Body Temperature

1
Get a digital BBT thermometer. You can buy a digital BBT thermometer at your local drugstore or the health aisle of your local supermarket. It will be labeled as thermometer specifically made for basal body temperature (BBT) readings. A digital BBT thermometer will allow you to get a quick, accurate reading. It will also beep when it has recorded your temperature and provide an easy to read number, which can be handy when you are sleepy in the morning.^{[1]
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- Some digital BBT thermometers also store the temperature for you. However, you should still record the temperature in a more permanent way, such as in a BBT journal or in a BBT app on your smartphone.
- You can also use a non-digital BBT thermometer as long as the thermometer is made to measure your basal body temperature, such as a glass thermometer.
2
Keep the thermometer by your bed. You will need to set up a routine in which you take your basal body temperature first thing when you wake up and are still lying down, before you move, stretch, or even talk. The idea is to get an accurate reading of your body at rest, and moving or talking can lead to a false BBT reading. To make it easier to take your temperature first thing in the morning, place the BBT thermometer next to your bed on a bedside table so it is handy when you wake up.^{[2]
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- If you are using a glass thermometer, make sure you shake it down at night before you place it on your bedside table. This way, it will be ready to use when you wake up.
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3
Take your temperature as soon as you wake up, at the same time every day. Try to take your temperature at the same time every morning. Set an alarm and try to stay within half an hour of your average time so your temperature does not vary too much from day to day.^{[3]
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- Always make sure you get at least three to five hours of continuous sleep before you take your basal body temperature to ensure the reading is accurate.^{[4]
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4
Put the thermometer in your mouth to take the reading. You can take your basal body temperature by putting it in your mouth in the same location every morning. Keep it in your mouth for several seconds to allow the thermometer to get an accurate reading.^{[5]
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- Some women take their basal body temperatures vaginally or rectally, especially if they find it difficult to get an accurate reading using the oral option. Make sure that no matter which method you chose, you stay with the same method for the duration of your cycle. Always place the thermometer in the same spot and at the same depth vaginally and rectally.

Part 2

Part 2 of 2:

Charting Your Basal Body Temperature

1
Record your BBT right away. To track your BBT effectively, you should write down the reading in the morning. Do this in a journal or on your phone using a tracking app. There are several apps available that will plot your readings on a chart or graph. You can then use the chart to get a better sense of your cycle and your ovulation periods.
- Make sure the chart includes a vertical section for the day of your cycle (1,2,3, etc), the month, and the date. It should have an horizontal section with a temperature range of 99°F to 96°F. Before ovulation, a woman’s BBT averages between 97°F (36.1°C) and 97.5°F (36.4°C). After ovulation, it usually rises 97.6°F (36.4°C) to 98.6°F (37°C).
- You can view a sample BBT chart online.^{[6]
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2
Check the chart after two cycles and look for any patterns. You will need to chart your basal body temperature for at least one to two cycles to get an accurate picture of your fertility. You should note any clear patterns on the charts, such as a temperature rise or fall at the same time in your cycle for both months.^{[7]
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- Notice if there is a temperature shift of at least 0.4 degrees within 48-hours on your chart. This is a sign that you are ovulating. The temperature shift should be higher than the highest temperatures that you recorded the previous six days. Most women have a basal body temperature of 96 to 98°F (35.6 to 36.7°C) one to two days before ovulation.^{[8]
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3
Identify the most fertile times in your cycle. For most women, the most fertile period is two days before their basal body temperature rises or they begin ovulation. Keep in mind sperm can live up to five days in your reproductive tract, so if you would like to get pregnant, you should have sex two days before you begin ovulating. If you do not want to get pregnant, you should avoid having sex from when your menstrual period starts until three to four days after your basal body temperature rises, though you should not rely on this as a form of contraception until you have tried it for a few months.
- If your basal body temperature stays up for more than 18 days after you have ovulated, you should get tested for pregnancy.^{[9]
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