Follow these steps to chart your basal body temperature (BBT):

  1. Start keeping track of your temperature on the first day of your menstrual period (first day you see red blood).
  2. Use a special basal body thermometer (mercury thermometer), which shows precise changes of 1/10 of a degree in your temperature.
  3. A digital thermometer can also work, although it's not as accurate and the 1/100 degree changes can be confusing.
  4. Changing a thermometer mid-cycle may change the accuracy of the curve.
  5. The temperature can be taken either in your mouth or the rectum or even the vagina. In the same cycle they should always be taken in the same place.
  6. Take your basal body temperature before you get up and after at least 3-4 hours of continuous sleep, preferably at the same time each day.
  7. Do not move, do not eat, do not drink, and do not smoke before you take your temperature.
  8. Immediately after taking your temperature write it down on the BBT chart or online in your FertilChart.
  9. On the day of ovulation there is sometimes, but not always, a drop in temperature. Most women don't have it.
  10. About 1-2 days after ovulation there is usually an increase in temperature by at least 0.2 degrees, and it stays up thereafter. That's called a 'biphasic' chart. 
  11. Calculate your coverline after you have detected ovulation.
  12. In a typical biphasic (=ovulation) chart, the temperature usually stays up until your next menstrual period.
  13. Basal body temperatures sometimes drop a couple of days before or after your menstrual period comes.
  14. When your menstrual period has come, you should indicate in the "Bleeding" row on your chart at the end of your cycle that it has come (an 'M' is seen). This allows us to calculate the cycle length and the corpus luteum phase (time between ovulation and next menstrual period).
  15. If there is no menstrual period and the temperature stays up longer than 15 days, that's a good indication that you may be pregnant.
  16. It's not recommended to adjust your temperatures. Please follow guidelines and chart your temperature exactly as it shows up on the thermometer.