How to chart your Basal Body Temperature (BBT)

Basal Body Temperature (BBT) charting helps you chart your fertility patterns. It can be done very easily. All you need is a BBT chart and a BBT thermometer.

Basically, what you are doing is taking your temperature, first thing each day and plotting the temperature on a chart. What you are looking for is, a shift of at least 0.4 degrees Fahrenheit, after the ovulation, making your chart biphasic (showing low temperatures before ovulation in the follicular
phase, and higher ones after ovulation in the luteal phase).

Why do you need to chart your basal body temperature?

A slight increase in basal body temperature is seen after ovulation. Hence, by keeping a track of your BBT, you can figure out the exact days of the month when you ovulate.

BBT charting and surrogacy

In case of a woman, who wishes to have children through surrogacy, BBT charting is required to find out her ovulation patterns and then align it with that of the surrogate’s. This is needed because when the oocyte/egg transfer is done from the genetic mother to the surrogate, both women’s cycles need to be in perfect harmony.

The steps below will help you read your BBT and analyze it:

1. Take your temperature first thing in the morning before you get out of bed or even speak. Leave the thermometer at your bedside, within easy reach, so that you don’t have to move much to get it. If you use a glass thermometer, make sure you shake it down before going to bed.

2. Try to take the temperature at as close to the same time each day as possible. Set an alarm if you need to. Staying within a half hour, on either side of your average time is a good idea because your temp can vary with the time (i.e., if you usually take your temperature at 6 a.m., it is OK to take your BBT between 5:30-6:30 a.m., but the closer to 6 a.m. the better).

The normal variation is by up to 0.2 degrees per hour — lower if you take your temperature early, higher if you take it late.

3. It is best to take your BBT after a minimum of 5 hours sleep, and at least 3 in a row is preferable.

4. You can take your temperature orally, vaginally, or rectally, just stay
with the same method for the entire cycle.

5. You should try to place the thermometer the same way each day (same location of your mouth, same depth vaginally and rectally).

6. Plot your temperature on your chart each day, but refrain from reading too much into it until the cycle is done.

7. Some women, not all, have a temperature drop when they ovulate.

8. What you are looking for is a temperature shift of at least 0.4 degrees over a 48-hour period to indicate ovulation. This shift should be above the highest temperatures in the previous six days, allowing one temperature to be thrown out as inaccurate (fluke, illness).

9. After you see a temperature shift for at least three days, or at the end of your cycle, you can draw a cover line between your follicular phase and luteal phase temperatures. With luck, it is easy to see a clear shift and draw your line between the highest follicular phase BBT and the lowest luteal phase BBT. The main reason for drawing this line is to clearly delineate that your chart is biphasic.

10. Look at the chart at the end of the month to analyze what happened.

11. Chart for at least two months and look for patterns.

You will be required to do your BBT Charting for at least 2 months. It can be done in the comfort of your home.

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