Basal Body Temperature and Ovulation: How To Track Your BBT

Here's how to measure your basal body temperature and why you should be tracking changes if you're trying to get pregnant.

By Parents Editors

Updated on May 9, 2019

Ovulation: Charting Your Basal Body Temperature

Your body gives you several signs that you could be ovulating. One is a change in your basal body temperature. Here are some frequently asked questions about basal body temperature and its relationship to ovulation.

What is your basal body temperature?

Basal body temperature is your body temperature when you're completely at rest, according to Planned Parenthood. Most women experience a slight rise in basal body temperature — measuring only fractions of a degree — when they ovulate. If you take your basal body temperature properly and chart it each day, it's possible to determine if ovulation has occurred.

But how can you measure such a small change in temperature? You need a basal body thermometer, a special, large-scale, easy-to-read thermometer that registers only from 96 to 100 degrees. Most women register 96 to 98 degrees before ovulation and 97 to 99 degrees after ovulation.

How do you measure basal body temperature?

To create an accurate chart, you need to take your temperature as soon as you wake up and at approximately the same time each morning. You must take your temperature before you get out of bed, talk, eat, drink, have sex, or smoke in order to get an accurate reading. The basal thermometer should be inserted for a full five minutes, and the reading should be recorded within one-tenth of a degree.

You can get a basal body temperature chart from your gynecologist. Keep your chart and a pencil by your bed and record your temperature within one-tenth of a degree each day. As your chart evolves you'll begin to see a pattern. Each person's pattern is different: some rise suddenly, while others increase more gradually. Patterns can also vary from cycle to cycle.

What should my basal body temperature be after ovulation?

When your basal body temperature rises higher than the temperatures you've recorded in the past six days, and stays at this level or increases for at least three days, it's likely that ovulation has occurred. In general the temperature range after ovulation is between 97 to 99 degrees — at least two-tenths of a degree greater than your temperature was during the previous week.

How do I know if I'm getting an accurate temperature reading?

There are factors that could cause your temperature to increase, thereby affecting the accuracy of your chart. These include:

Lack of sleep or disturbed sleep
Illness or exhaustion
Emotional distress
Smoking
Alcohol consumption
Sleeping with an electric blanket

If you experience one of these factors, it should be noted on your chart to help clarify the reading. It might take several cycles before you determine an accurate indication of ovulation. It's best to use the basal body temperature method in conjunction with monitoring of your cervical mucus and other physical signs of ovulation, and with an ovulation predictor kit (available in most drugstores).

To be certain that you're getting the best results, carefully follow the instructions that come with your basal body temperature thermometer, and make an appointment with your health-care provider to answer any questions you might have about the charting process and about interpreting your chart.

Source: Planned Parenthood Federation of America

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