Rule of thumb: Day one of the cycle is the first day of menstrual bleeding.
Normally, the first half of the cycle the temperatures are in the low range, anywhere from 96.0 F to 98.0 F. This is due to the hormone estrogen. Ovulation occurs sometimes around the middle of the cycle (but can be as soon as day 8 or much much later.) After ovulation the temperature will shift upwards, normally about .4 of a degree. This indicates that an egg has been released. Usually by the time you see the temperature shift, the egg has either been fertilized or has died.
Progesterone is the hormone that is released after ovulation. Progesterone will start in production while the egg is moving through the fallopian tube. The higher temps will stay this way through the length of the luteal phase - the time from ovulation till menstruation. This time will vary from woman to woman. Normally it averages around 12 to 14 days.
You must have a good basal body thermometer. You can buy these at most any store that sells pharmaceutical supplies. It's important to take your temperature at the same time every morning. Make sure you have slept for at least 3 hours prior to waking up. Take your temperature before moving around or talking.
When you start our ovulation chart calendar for fertility you count the first day of bleeding as day one on the chart. You mark on the chart the days you bleed and or spot. Mark on the chart your temperatures and the time you took them each morning. You can also mark if you had other issues such as headache or cramps, etc.
If you find that you take your temperature at a different time from you established time you can:
This has to be done because the basal body temperature will creep up as the day gets started.
The factors that can affect your BBT are:
If any of these occur, again, note them on your chart.
You will only know ovulation has occurred after the fact, when you see the temperature shift upward. Keeping the ovulation chart calendar for fertility handy to record your basal body temperature is a good idea. A good chart will have areas to record other fertility symptoms as well.
Once you see the upward temperature shift, look at the last six temperatures correctly and draw a line one tenth of a degree above the highest of the previous six. This will be your "coverline". Your post ovulation temperatures should stay above this line during the luteal phase. If it doesn't, this is indications of possible problems such as luteal phase defect, thyroid dysfunction, etc.