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Charting Basics: Basal Body Temperature

Lori Ramsey


Basal body temperature (referred to as BBT) is the temperature the body is at rest. BBT can tell a woman a lot about her fertility cycle. Charting temperatures helps a woman to know when she has ovulated, and possibly even if she is pregnant. It can also tell a woman if she has a problem, such as not ovulating - called anovulation and low progesterone and thyroid dysfunction.

The first two weeks or so, the temperature is in the low range - anywhere from 96.0 to 98.0 - though some women will be a little higher. This is due to the hormone estrogen. After ovulation occurs, the temperature has what is called a shift upward, usually about .4. This is indicating that the egg has been released, and usually by the time you see the temperature shift - the egg has either been fertilized or has died. Progesterone is the hormone released after the egg has moved into the fallopian tubes. The higher temps will stay this way for the length of the luteal phase - the time from ovulation to menstruation. This will vary from woman to woman. Usually it averages around 12 to 14 days.

In order to effectively chart your temperatures, you need to have a good basal body thermometer. A fever thermometer is not good to use, because it won't tell the temperature to the .1 degree like a basal body thermometer will. In my experience, I think the digital ones are as good as the glass ones - however I have read conflicting advice on this. It's very important to take your temperature every morning, at the same time. And it's very important that you have slept at least three hours prior to taking your temperature. Take your temperature before rising and before moving around very much -as these things tend to affect the true temperature. Be sure to start your chart on the first day of your cycle - the first day of actual bleeding.

A good rule of thumb to use is that if you wake up earlier or later than your scheduled time, add .1 degree for every half hour early you awaken and to subtract .1 for every half hour you awaken late. This is because the basal body temperature will creep up as the day gets started.

There are factors that can affect your BBT, such as sleeping with your mouth open, having your feet outside the covers, having it too cold or too warm in the room, snuggling with your partner and/or being sick. If any of these occur - note it on your chart.

You will not really know when ovulation occurs until after the fact when you see the temperature shift upward. Have a good chart handy to record the temperatures on every day. A good chart will have areas to record other fertility symptoms as well, which I plan on covering in upcoming weeks.

Once you see the temperature shift - look at the last six temperatures that were taken right, and draw a line one tenth of a degree above the highest of the previous six. This is called your coverline. Your temperatures should stay above this line post ovulation. I will discuss, at later dates, possible problems with temperatures that stay at or below the coverline - causing what's known as luteal phase defects.

Related Articles

Charting Basal Body Temperature: How to Chart Yours

Charting Basics - Cervical Fluid

Charting Basics - Cervical Position

Charting Cervix Position

Fertility Charting: A Beginner's Guide


Showing 1 - 10 out of 23 Comments
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Kar Mar 11, 2019 11:02:14 PM ET

I'm TTC and on day 23 of my cycle having cramps and brown spotting. Could this be implementation bleeding. I'm Not due for my period for another 6 days?

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Precious46 Jan 3, 2019 11:39:45 PM ET

Oh, I forgot to mention, been nauseous as well.

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Precious46 Jan 3, 2019 11:37:21 PM ET

Hello, I had my period 12/17/18 until the 21st and 12/28/18 was my estimated ovulation date. Me and my boyfriend engaged in sex Thurs, Friday, and Saturday. Today I started having this light cramping and spotting. It started off light pink and now brown, and it's fading away. I have on a liner. Could I be pregnant?

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Cia76 Dec 18, 2018 08:14:37 PM ET

Hello! My period was on 8/13/2018 the week after was my fertile days. I had implantation bleeding on 9/3/2018 cycle day 22 and 9/4/2018 cycle day 23 and on 9/5/2018 cycle day 24.9dpo! On 9/10/2018! Cycle 28! Boom no period! So I was just wondering, with everyone's help on here, could I be pregnant?

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SUGI Aug 16, 2018 04:46:42 PM ET

I am 7dpo and I am having strange vagina tightening and it even shoots pain to my buttocks.

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Guest Mar 28, 2018 12:45:03 AM ET

I had an irregular cycle in this past month, it lasted 2 days and spotted on and off for 9 days and quit. This changed my cycle from 31 days to 27 days. Since it started 4 days early also and I had unprotected sex I tested negative for pregnancy. But, I had unprotected sex on the 8th day of my 27 day cycle this time and I ovulated by the looks of my discharge on the 22nd of March. Could I be pregnant? My cycle isn't due until April 8th.

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Leana Feb 22, 2017 05:27:58 AM ET

No implantation, can I be pregnant?

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yesha Sep 23, 2016 02:44:28 PM ET

I had an irregular cycle. July 4th, I got my period for June. And had sex on July 19th and 22nd. I got my next period for July on August 10-13. Now I haven't got any period for the month of August and I have a 6 day spotting. Mild cramping, higher temp (I think). Am I pregnant?

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arlena Feb 1, 2015 05:31:28 PM ET

I had my baby girl on Aug 4, 2004 and had my tubal cauterization done on DEC 14, 2004. I ovulated on Nov 23, 2014, and I had my last period on Dec 2, 2014. I missed my other period on Dec 30, 2014 and I ovulated on Jan 14, 2015. I had implantation bleeding on Jan 20th through the 24th. My period was suppose to come on Jan 27, 2015. I still didn't see it. Could I be pregnant?

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jaz Dec 1, 2014 09:30:43 AM ET

I had intercourse 2 days before I was ovulated and that's it. My period came on 11/12/14, and I ovulated between the 23rd and 28th. Could I be pregnant?

Allie Dec 6, 2014 03:00:00 PM ET

My doctor says that sperm can service in the uterus for up to 5 days, so i would have to think that it's possible.

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