Charting Basics: The Rule of Thumb

By JustMommies staff

Occasionally you will have a temperature that is really high. This can throw things off when you are trying to draw your coverline or determine ovulation. If you have a fever, wake up late, or drink alcohol it may cause your temperature to rise. If you are new to charting you may wonder what you should do with these temperatures. If you have an artificially high temperature it is best to apply the rule of thumb.

What is the Rule of Thumb?

If you have an artificially high temperature put your thumb over the temperature. Leave the temperature on your chart just don’t use it to determine your coverline.

Coverline and Rule of Thumb

Drawing your coverline is easy. You will want to look for a rise of at least .2 degrees F on your chart. Once you see this rise in temperature you can draw your coverline. You normally count six days back from the time you see this rise in temperature to draw your coverline, but if you have a temperature that is unusually high, put your thumb over this temperature and then draw your coverline based on the six temperatures prior to the rise.

How to connect your temperatures

If you have a temperature that is out of the ordinary and you decide to apply the rule of thumb, you will not want to use this temperature when you are connecting the temperatures on your chart. Instead of drawing a line between each temperature, like you normally do, draw a dotted line between the two temperatures on either side of your “rule of thumb” temperature.

If I oversleep should I adjust the temperature or use the Rule of Thumb?

Some women adjust their temperature when they oversleep. Generally, waking temperatures rise about 1/10 of a degree for every half hour you sleep in. You can adjust your temperature but it may make your chart inaccurate. It is safer to apply the Rule of Thumb if you have an unusual temperature.