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Basal temperature

Basal temperature (Basal Body Temperature, BBT) is the body temperature in the morning before rising or moving around or eating anything.

Basal temperature can be observed to assist you in checking your fertile days and/or fertile status. It is useful for telling you that you have ovulated but not much good at warning you that ovulation is going to happen.

Using Basal Temperature method you can identify the slight drop before ovulation and then rise by 0.5 degree Celsius or 1 degree Fahrenheit after ovulation has occurred. It remains raised until your next menstrual bleeding, when it will drop again, to start the cycle again.

Thermometer for basal temperature

Basal Temperature is measured by taking your temperature in the normal fashion each morning as soon as you wake up and before you do anything else (including going to the toilet, having a cup of coffee, discussing morning issues, etc.). You can write the temperature down on your chart, and soon you will notice a pattern.

1. Charting your BBTs is really pretty easy. Basically, what you are doing is taking your temperature first thing each day and plotting the temperature on a chart.

2. Check your basal temperature every morning as it is advices above – as soon as you wake up and before you do anything else (including going to the toilet, having a cup of coffee, discussing morning issues, etc.).

3. Try to take the temperature at approximately the same time each day. Staying within an hour either side of your average time is a good idea because your temperature can vary with the time.

4. It is recommended to take your basal emperature after a minimum of 5-6 hours sleep.

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

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

7. Register your basal temperature on your BBT chart each day.

Basal temperature

8. Some women, not all, have a temperature drop when they ovulate. If you see this drop, it is a good idea to have sex in case you are ovulating and in case you are planning pregnancy.

9. What you are looking for is a temperature shift of at least 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 (stress, fluke, illness).

10. 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 as in the sample above. The main reason for drawing this line is to be sure that your chart is clearly biphasic. If not – most probably you did not have ovulation which could be temporary (not very important) but it also could be a reason for infertility (if you had 2-3 months if monophasic basal temperature).

11. The analysis should be done at the end of the month (end of menstrual cycle!) to be able to understand the whole picture. One month chart is not enough for analysis; you would need few months’ charts to be able to recognize patterns.

12. If your temperature stays up for 18 days or more after ovulation, it could mean the pregnancy – be careful and test for pregnancy.


Women with ovulatory cycles but with irregular cycle lengths usually have different duration of the follicular phase (first part of the chart). The luteal phase should be relatively constant (within 1-2 days). So if one has a cycle that ranges from 28-34 days, and a luteal phase of 14 days, ovulation would occur somewhere between days 14-20 – not the middle of a cycle (not i the middle of cycle). This is the biggest mistake women with long cycles make when trying to conceive.

Basal temperature during pregnancy


If your basal temperature stays high for 18 days or more after ovulation, it could be first signal for pregnancy – be careful and test for pregnancy.

Discover basal temperature during pregnancy on next page.


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