How Basal Body Temperature Charting Can Help You Get Pregnant

Woman taking her body basal temperature
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Your basal body temperature is your body's temperature at complete rest. When you ovulate, your basal body temperature rises slightly. You can use this information to detect ovulation and potentially get pregnant faster.

Charting your basal body temperature is a relatively easy and inexpensive way to track ovulation. All you need is an accurate thermometer, a fertility charting app or program (there are lots of free ones available), and some patience.

What Is Your Basal Body Temperature? 

While you might think of your temperature as either being normal or feverish, there are a lot of normal variations in between. Our body temperature changes based on movement, how much sleep you've had, the time of day, exercise levels, and hormonal changes. 

After you ovulate, the hormone progesterone begins to rise. Progesterone causes a slight increase in temperature. You can detect this change by charting your basal body temperature.

The upward shift caused by ovulation is at least four-tenths of a degree. For example, 98.4 is four-tenths higher than 98.0. If this upward change stays around for at least three days, you can be pretty sure that ovulation occurred on the day before the temperature rise.

Basal Body Temperature and Getting Pregnant

To get pregnant, you need to have sex before the shift occurs. Your chart can help you see when you ovulate each month, so you can time sex for conception better. For the best results, you should also look for other ovulation signs like cervical mucus and mark them on your fertility calendar

If this sounds complicated, don't worry. Most fertility charting programs do the hard work—like figuring out when you ovulated and when you might ovulate next month—for you. All you have to do is take your temperature correctly and input your information.

How to Take Your Basal Body Temperature Correctly

Because the shift you're looking for is so small, it’s important to take your temperature at the same time every morning before you get up or move. You will need a basal thermometer that displays at least one-tenth of a degree. Just about every thermometer you can buy at the pharmacy does this. 

Once you've got the right kind of thermometer, here's what to do next:

  1. Before you go to bed at night, place a thermometer within your reach by your bed. You need to be able to reach it without sitting up or moving around. Getting out of bed will throw off your readings and skew your results. 
  2. If you're using a mercury thermometer, shake it down before bed. Don't plan to shake it down in the morning, as that can increase your body temperature.
  3. Set your alarm for the same time every day. Yes, even on the weekends. An extra hour or two of sleep will throw your chart off. Aim to take your temperature within the same 30-minute window every morning.
  4. When you wake up, reach for the thermometer and take your temperature. Do not go to the bathroom or even sit up first.
  5. Take your temperature orally or vaginally. There isn't a difference in which method you use, as long as you're consistent. Orally is the easiest (and more comfortable for many people). But if you sleep with your mouth open (which can throw off your temperature reading), you may want to go the vaginal route. 
  6. Follow the directions for your thermometer to get the best reading. If you’re using a mercury thermometer, make sure you leave it in place long enough to get a final reading. That may take up to four or five minutes.
  7. After you take your temperature, write it down. Keep a notepad and pen by your bedside to make this simple. Another option is inputting your result right into your smartphone if you're using a fertility app. Some basal body temperature thermometers also come with a memory function.

Other factors to keep in mind:

  • If you need to wake up extra early, or later than usual, take your temperature as you always do. Mark the difference in time on your chart. Yes, it won't be as accurate, but being one day off isn't a big deal as long as you're consistent most of the time.
  • You need to have slept at least four straight hours for your temperature to be accurate. Getting up often at night or have trouble sleeping can throw off your results. You should take your temperature anyway, and note that your sleep was interrupted on your chart.

Charting Your Basal Body Temperature

Taking your temperature is only part one. You can't do much with just one basal body temperature reading. You need a consistent series of them, and you need to record them somewhere. 

One of the most efficient ways to track your basal body temperature is with a fertility charting app or computer program. You won't have to worry about whether your temperature is sustained long enough or not, or spend time calculating when you might be most fertile the next day. The software will do that for you. You can also do your charting by hand on graph paper.

Tracking Cervical Mucus Changes on Your Chart

Another great thing about basal body temperature charting is that you can share your charts with your doctor. If it seems you're not ovulating, or if your luteal phase looks too short, you can share this information easily with your doctor.

The problem with only looking at your basal body temperature is that it only tells you if you ovulated after it happened. But you need to have sex before ovulation to get pregnant. Your basal body temperature can't warn you that ovulation is coming. Changes in your cervical mucus, however, can.

Cervical mucus is produced near your cervix, but you don't need to reach up to your cervix to see it. You may see it on your underwear, when you wipe after urination, or you can actively check for it by placing a finger into your vagina. Tracking your cervical mucus changes is easy to do, and it is sometimes easier than charting your temperature. Also, most fertility charting apps allow you to put this information into your chart.

Your cervical mucus will change throughout your cycle, going from dry and crumbling to creamy, wet, and, finally, to the consistency of raw egg whites. When your vaginal discharge resembles a raw egg white, this is when you're most fertile and about to ovulate. This is the best time to have sex to conceive

In addition to tracking mucus changes, you can also track changes in your cervical position. This is slightly trickier and has a steeper learning curve, but it may still be worth looking into.

Possible Downsides to Basal Body Temperature Charting

Basal body temperature charting is not for everyone. It may not be for you if:

  • You work night shifts
  • You have to get up often in the night with young children
  • You can't get up at around the same time each day
  • You feel stressed needing to track your temperature

Charting may be all the rage on fertility forums, but you can still get pregnant without it. There are other signs of ovulation you can watch for, such as increased sexual desire. You can also try using ovulation predictor tests, or just choose to have sex three to four times a week.

At the same time, if you're using the charting method to try to avoid pregnancy, you need to be diligent and disciplined about keeping at it. You'll need to also plan to use contraception if you decide to have sex during your fertile days.

Lastly, some women won't see a sustained rise in temperature, even if they do ovulate. If this applies to you, you should mention it to your doctor to determine whether there are other underlying health issues you need to address. 

A Word From Verywell

Some women find charting to be an empowering way to learn about their bodies and increase their odds of getting pregnant. The act of taking their temperature and charting may give them a sense of control and confidence with regard to their fertility. For these women, basal body temperature charting is often a positive experience.

But if you feel stressed and overwhelmed by charting procedures and results, it may not be for you. The act of timing sex for ovulation (as opposed to having sex frequently and not trying to specifically time intercourse for their fertile window) can add more stress and be a negative experience for some couples. Remember that charting is a choice and there are other fertility tracking options available to you.

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Article Sources

Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Su HW, Yi YC, Wei TY, Chang TC, Cheng CM. Detection of ovulation, a review of currently available methods. Bioeng Transl Med. 2017;2(3):238-246. doi:10.1002/btm2.10058

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