You’ve likely heard that a fever is a temperature of 100.4 Fahrenheit or above, but your basal body temperature (BBT) is something different altogether. While checking for fever can be done at any time of the day, checking your BBT can only be done before you get up in the morning. 

Your BBT is your body’s temperature as soon as you wake up, before you get out of bed, or do anything at all. When you ovulate, your daily temperatures rise about 0.5 degrees Fahrenheit above the temperatures before ovulation. They stay elevated until you either get your period (at which point they drop) or become pregnant (when they continue to stay elevated).

What is a normal BBT?

Your normal BBT temperatures stay more or less stable, and they’re often different within a narrow range from one woman to the other. 

• Normal pre-ovulation temperatures: They can range between 97°F (36.1°C) and 97.5°F (36.4°C), but could be a little higher or lower, too. 
• After ovulation: Your BBT usually rises by about 0.5°F (0.3°C) to about 97.6°F  (36.4°C) to 98.6°F (37°C). That is called a biphasic temperature. 
• When you’re not pregnant: Your elevated temperatures after ovulation usually stay elevated until you get your period (which means you’re not pregnant), and they drop to what they usually were before ovulation. 
• When you’re pregnant: The temperatures usually stay elevated for longer than 15-16 days.

What about a BBT that is much lower or higher than the average?

A BBT that is too low is consistently below 96.4°F (35.8°C) and a BBT that is too high is above 99.5°F (37.5°C). Keep in mind that these are your BBTs, and not your waking/moving temperatures. 

These temperatures can happen normally if you sleep in a room that is colder or warmer, and it’s usually not a concern as long as you feel fine. However, if you don’t feel well, it’s a good idea to discuss this with your doctor.