BBT Chart Tool
Enter your daily basal body temperature readings to create a chart, identify your thermal shift, and estimate ovulation.
Understanding BBT Charting
What Is Basal Body Temperature?
Basal body temperature (BBT) is your body's lowest resting temperature, taken first thing in the morning before any physical activity. During your menstrual cycle, BBT follows a predictable pattern driven by hormonal changes. Before ovulation, during the follicular phase, your BBT tends to be lower, typically between 97.0-97.5°F (36.1-36.4°C). After ovulation, progesterone causes a rise of about 0.2-0.5°F (0.1-0.3°C), and your temperature stays elevated throughout the luteal phase until your next period begins. This rise is called the thermal shift and confirms that ovulation has occurred.
How to Measure BBT Accurately
For the most reliable BBT readings, follow these guidelines: • Use a basal thermometer that reads to 0.01 degrees for precise measurements • Take your temperature at the same time every morning, immediately upon waking • Measure before getting out of bed, eating, drinking, or talking • Get at least 3 consecutive hours of sleep before your reading • Use the same method (oral, vaginal, or under the arm) consistently • Record the temperature right away to avoid forgetting Factors that can affect your reading include alcohol consumption, illness, poor sleep, travel across time zones, and certain medications. Note any disruptions alongside your temperature so you can account for them when reading your chart.
Reading Your BBT Chart
A BBT chart reveals several important pieces of information about your cycle: Coverline: This horizontal reference line is drawn at the level of the highest of the last 6 pre-ovulation temperatures. Temperatures that stay above this line after ovulation confirm the thermal shift. Thermal shift: The point where your temperatures rise and stay elevated. This typically happens the day after ovulation. A sustained rise for 3 or more days confirms ovulation. Biphasic pattern: A healthy ovulatory cycle shows two distinct temperature phases — lower before ovulation and higher after. If your chart remains flat (monophasic), ovulation may not have occurred that cycle. BBT charting is most useful for confirming ovulation after it happens and understanding your cycle patterns. For predicting upcoming ovulation, combining BBT with other signs like cervical mucus is more effective.
Frequently Asked Questions
Smarter Temperature Tracking
Cyla uses AI to analyze your BBT patterns, predict ovulation, and sync with your full cycle data. Free to download.
