Troubleshooting Basal Body Temperature for Fertility Charting

“My basal body temperature isn’t reliable.” I hear this a lot, with a lot of different reasons following, depending on the person. Quite a lot of people give up on charting their temperature to identify ovulation. Most of the time they hadn’t tried any troubleshooting to figure out the problem first.

Sometimes the answer is as simple as, they haven’t yet learned how to interpret their temperature to identify ovulation. Other times they just weren’t aware of the various factors that can impact temperature but are easily fixed!

There are evidence based guidelines to identifying ovulation in your basal body temperature patterns. It’s not just about looking for a temperature that’s higher compared to the rest. Or about looking for multiple days of high temperatures compared to the rest. If you don’t yet know how to determine that ovulation has passed based on your temperatures, then I recommend considering taking my fertility awareness class to learn more.

How do you know if you need to troubleshoot your temperatures?

Most often troubleshooting needs done if there are big jumps between temperatures from day to day. I consider an erratic pattern to be .4 degrees fahrenheit (or .2 C), or more, between temperatures from day to day. More than just one or two days out of the cycle. Some people may experience this more in one phase of the cycle than the other.

I was actually able to confirm ovulation in this cycle using a different thermometer. This temperature chart was done using a fever thermometer and an irregular schedule. A bad combination for stable temperature patterns. A great example of what you might see in unideal conditions.

It’s important to remember that there are a lot of things that can impact your temperature. Alcohol the night before can lead to a raised temperature in the morning. Especially if you drink more than normal. Any kind of travel, even if it’s not across time zones (but especially across time zones!) can lead to jumpy temperature patterns. Illness or injury of any kind, even if you didn’t have an obvious fever. Some medications may also impact things.

If any of these factors have impacted your temperatures, be sure to make a note of it in your chart and mark the temperature that day as invalid (disturbed or questionable are other terms your app might use). If you’ve ruled out any external factors, it’s time to take a look at your temperature taking routine.

Get the Most Out of Your Basal Body Temperature

Let’s start with the most ideal situation for taking your basal body temperature for fertility charting:

  1. Use a basal body thermometer that reads to the hundredths.
  2. Round your temperatures when charting.
  3. Use a basal body thermometer that reads your temperature for at least 3 minutes.
  4. Take your temperature at the same time every morning.
  5. After getting at least 3 hours of sleep.
  6. Before getting out of bed.
  7. With the bulb of the thermometer placed under your tongue, in the same spot every day.

Okay, let’s be real. For a lot of people, not all of these are possible. Does that mean charting basal body temperature won’t work for them? Absolutely not! Let’s break this down one by one.

1. Use a basal body thermometer that reads to the hundredths

Honestly, this is probably the only one that is non-negotiable. Especially if you’re not able to meet all of the other recommended factors. You want a basal body thermometer that reads to the hundredths for accuracy. A standard fever thermometer reads to the tenths, for example 98.6. A basal body thermometer reads to the hundredths, for example 98.67. Thermometers are proven accurate to the second to last digit. This means if a thermometer reads to the tenths at 98.6, you can guarantee your temperature is at least 98, but the .6 is an estimate. So for a thermometer that reads in the hundredths at 98.67, you can guarantee your temperature is at least 98.6 but that .07 is an estimate.

Ultimately, basal body thermometers are more sensitive.

2. Round your temperatures when charting.

This is a super simple step that a lot of beginners miss. It might seem confusing to round your temperatures after the heavy emphasis on the need for the thermometer to read to the hundredths. But rounding the temperatures on the chart can make it a lot easier to read.

Remember, the hundredths place is important for accuracy. You don’t lose that accuracy in rounding. You’re just simplifying things. Most people find that once they’ve rounded their temperatures, their patterns on the chart look a lot less erratic and are easier to interpret. Some apps will round for you if you tell it to in the settings.

This makes it easy to enter your temperature to the hundredths and let the app do the work for you. But if you’re using an app that can’t do that, I definitely recommend rounding the temperatures yourself.

3. Use a basal body thermometer that reads your temperature for at least 3 minutes.

Most people don’t actually follow this one. But in my experience, both personally, and in working with clients, going from a thermometer that only reads for 30-60 seconds to one that reads for 3 or more minutes, makes a big difference in the stability of the temperature pattern.

Most people can get away with having a shorter temperature taking time. But for others, it can lead to erratic temperature patterns that make it difficult to identify a temperature rise. Changing this factor is an easy fix. See my post on The Best Basal Body Thermometers to find one with a longer temperature taking time. My favorite is the Femometer Vinca II set to Mercury Mode.

4. Take your temperature at the same time every morning.

Ideally you’d want to take your temperature within 30 minutes of the same time every day. So if you set your alarm for 8 am, you could take your temperature any time between 7:30 and 8:30 and still get stable temperatures.

This one can be tricky. When I first started charting my cycles I was working a second shift job. That meant I had to be at work at 2:30 pm and could wake up whenever I wanted. I rarely woke up the same time every day. Nearly 2 years into charting, my schedule changed to starting work at 9 am. I had to wake up to an alarm, and even though I was snoozing regularly, I was taking my temperature within a shorter window. It definitely seemed to make for a smoother pattern.

These days I have an alarm set for 6:30. I take my temperature and then go back to sleep until I’m ready to wake up for the day. (It helps that I work from home and can sleep in if I want to). I love using the Femometer Vinca II because I can sync it to my phone when I wake up for the day and add it to my chart at that time.

I always recommend starting with what is normal for you and making adjustments if your temperatures are erratic. This is a good place to start your troubleshooting if you have an irregular schedule that can be changed. I know from experience that getting your temperature at the same time every day isn’t as hard as it first seems.

The method of charting that I teach actually provides a calculation to correct for time differences if it happens on the rare occasion. It’s definitely not something you should attempt without guidance though.

5. After getting at least 3 hours of sleep.

This one really depends on how sensitive the person is. I sleep pretty restlessly some nights. Sometimes it doesn’t make a difference in my temperature, and sometimes I end up with a really high temperature. If not getting 3 hours beforehand is normal for you, your temperature patterns might be able to handle it. But if less sleep is a change to your normal routine, or happens only every once in a while then you may see the impact in your chart.

And different methods have different recommendations on this. I’ve seen recommendations anywhere from 1 hour, to 5 hours. I believe the ideal is just to keep it consistent from day to day. I’ve known people able to get little sleep through the night and still get a usable temperature in the morning.

As always, start with what is normal for you, and make changes from there until you find the routine that leads to good temperature patterns.

6. Before getting out of bed.

So this one also depends completely on the person. It is ideal to take your temperature as soon as you wake up and before getting out of bed. As soon as you start moving, your temperature begins to rise. I have heard of some people keeping a consistent routine every day of taking their temperature on the way to the bathroom as soon as they’ve gotten out of bed and getting usable temperatures. Or some other similar scenario. The key here is just after they’ve woken up and that it is a consistent routine every day. It’s not ideal, but can be done if done very carefully.

Some people also ask if it’s okay if they get up and use the bathroom in the 3 hour period before their normal wake up and temperature taking time. Again, it depends on the person. I often get up to use the bathroom 1-2 hours before my alarm and as long as I go back to sleep in a reasonable amount of time then my temperature is not affected. Other people might see bigger impacts. My recommendation is to start out without any concern for what your temperature will look like. Go to the bathroom, holding it until your temperature taking time is silly, and not healthy! Over time you will be able to see what is normal and what isn’t. If you happen to have a high temperature that day, the trip to the bathroom may have disturbed it.

7. With the bulb of the thermometer placed under your tongue, in the same spot every day.

This one might seem like common sense but some people just don’t realize that it’s best to put it in the same spot under your tongue every day. Temperature varies throughout your mouth. Making sure you’re putting it in the same spot means making sure you get the most stable temperature from day to day. Under the tongue is the warmest location with the most consistent temperatures.

Another thing to consider under this topic is if you’re “mouth breathing”. Make sure that you keep your mouth closed while you’re taking your temperature. And, if you’re a person who breathes through your mouth while you sleep, that could potentially impact your temperatures as well.

You may not even be aware that you’re doing it. If you’ve gone through all the other troubleshooting steps and nothing seems to be helping, you may be mouth breathing while you sleep. Some people who mouth breathe prefer to use medical tape to keep their mouth closed at night. It sounds weird but it apparently has some health benefits. Or, alternatively, you could try vaginal temping.

Vaginal Temping

If you have worked your way through the troubleshooting steps, and have tried different thermometers, and you’re still seeing erratic patterns that are interfering with identifying a temperature shift, consider vaginal temping.

With this method of taking your temperature, you’ll just be inserting the tip of the thermometer into your vagina instead of under your tongue. The vagina is much warmer than the mouth and also has less variances in temperature.

When fertility awareness methods were first developed, rectal temperatures were one of the most commonly used modes of temperature taking. I would never want to try it, but it is an option!


I’ve never seen anyone NOT have success when trying the troubleshooting steps with diligence. But if absolutely none of the above has made a difference for you, you could try the Tempdrop. I only ever recommend this as a last resort and you can read why here.

Other Considerations

If you have tried all of the above and feel like your temperatures are still erratic, it’s possible that it’s a hormonal issue. Stress is one common factor that can lead to such jumpy temperature patterns. Adrenal issues and PCOS are also common reasons. At this point it’s worth doing some health investigations.

Want One on One Support?

I am always available to help you through troubleshooting if you’re feeling lost on how to correct confusing temperature patterns. I offer hourly consultations for chart reviews and discussing any questions or concerns you have surrounding your charts.

Have you ever successfully improved your temperature patterns? Let me know in the comments what you did that helped!



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