Basal Body Temperature (BBT) Charting Introduction 101

    Learn how to start charting your Basal Body Temperature (BBT), improve your chances of getting pregnant and find out if and when you ovulated and if you had intercourse at the right time.

    1. Get a basal body thermometer (you should be able to get one at your local drugstore) that shows precise changes of one-tenth of a degree in your temperature.
    2. Some doctors suggest using a glass or mercury thermometer because they feel it's more accurate. But in most cases a special digital thermometer is fine for taking the BBT. The digital ones have advantages: They are harder to break; some may remember the temperature for you if you don't want to chart it immediately; they beep when it's ready for use; and you don't have to shake down the thermometer after taking your temperature.
    3. Start keeping track of your temperature on the first day of your period (first day you see bright red blood).
    4. The temperature can be taken either in your mouth or the rectum (or even in the vagina). But you must take it always the same way throughout the menstrual cycle and preferably with the same thermometer.
    5. Don't switch thermometers mid-cycle.
    6. Do not move, do not get out of bed, do not eat, drink, or smoke before you take your temperature.
    7. Take your temperature at the same time each day (within 30-60 minutes is fine).
    8. Have at least 3-4 hours of consecutive sleep when taking your temperature.
    9. If you get up earlier or sleep in later, take your temperature as usual and make note of the time. We do not suggest "adjusting" a temperature just because you may have taken it earlier or later than usual.
      Sleeping for a shorter time period or drinking alcohol the night before may affect the accuracy of the temperatures.
    10. Write down the temperature after you have taken it. Do it immediately after reading it, otherwise you might forget the temperature later on. You can record your temperature on a paper chart or by using the BabyMed FertilChart online charting software. Paper charts are usually included within the BBT thermometer package or available at your ob-gyn's office.
    11. Calculate your coverline after you have detected ovulation. I had you until that last part, right? The coverline is a horizontal line drawn after ovulation to help differentiate temperatures before ovulation (low) and temperatures after ovulation (high). When your waking body temperature rises more than two-tenths of a degree higher than the previous six days, and it stays that way for at least two days, your coverline can be established.