Your basal body temperature (BBT) is your lowest body temperature in a 24-hour period. You’ll need to measure it every day for a few months to see if there’s a predictable pattern to your cycle that will allow you to estimate when you’ll ovulate.
To get an accurate reading, you need to use a basal thermometer, which is sensitive enough to measure minute changes in body temperature. Some experts think glass BBT thermometers are more accurate than digital ones.
Take your temperature when you first wake up in the morning – before you eat, drink, have sex, or even sit up in bed or put a foot on the floor – and record it on a BBT chart. Try to take a reading at about the same time each morning. If you don’t take your temperature immediately after waking up, your BBT chart will not be accurate. The same is true if you get a fever.
Before ovulation, your BBT may range from about 97.2 to 97.7 degrees Fahrenheit. But the day after you ovulate, you should see an uptick of 0.5 to 1.0 degree in your BBT, which should last until your next period. You may notice your temperature occasionally spiking on other days, but if it doesn’t stay up, you probably haven’t ovulated yet. If you become pregnant, your temperature will stay elevated throughout your pregnancy.
After charting your BBT for a few months, you’ll be able to see whether there’s a pattern to your cycle. If there is, you may be able to estimate when you’ll next ovulate. Charting your BBT can also help your healthcare provider pinpoint the cause of fertility problems.