BBT Chart

Basal body temperature (BBT) is your body's temperature at complete rest, measured immediately upon waking before any activity. During the first half of your cycle (the follicular phase), BBT tends to be lower, typically ranging from 97.0°F to 97.5°F (36.1°C to 36.4°C). After ovulation, progesterone causes a sustained rise of about 0.4°F to 1.0°F (0.2°C to 0.5°C), which remains elevated until your next period begins. This thermal shift is the basis of BBT charting.

To get reliable readings, take your temperature at the same time every morning before getting out of bed, eating, drinking, or talking. Use a basal thermometer that reads to two decimal places for accuracy. Factors such as poor sleep, alcohol consumption, illness, room temperature changes, and waking at a different time can all affect your reading. Note these disturbances so you can account for them when interpreting your chart. The coverline, a horizontal reference line drawn on your chart, helps you visualize the temperature shift.

BBT charting is a retrospective method, meaning it confirms ovulation after it has already happened. It does not predict ovulation in advance. For this reason, ACOG and fertility specialists often recommend combining BBT tracking with cervical mucus observation or ovulation predictor kits (OPKs) for more complete fertility awareness. This tool is for educational and personal tracking purposes and is not a substitute for professional medical guidance. If you are trying to conceive or struggling with fertility, speak with your OB-GYN or a reproductive endocrinologist.