Mira vs BBT: Which is Right For You?

by Jul 1, 2020

In our series comparing different methods of tracking fertility we previously discussed OPKs. There are so many other methods out there to consider – from the most basic to the most scientifically advanced. This time we are going to go a little more basic and explore the use of basal body temperature tracking as a fertility awareness method.

Mira and BBT

The Basal Body Temperature (BBT) method is an inexpensive option with no side effects. Considered a more natural way to track fertility it is preferred by some women for religious reasons as well. This method tracks changes in your basal body temperature over time to attempt to detect when ovulation has occurred.

How it works

Your basal body temperature refers to your temperature when your body is at rest. Therefore, you need to take your temperature first thing in the morning before you get out of bed in order to get an accurate reading.

Note that you cannot even talk or sit up prior to taking your temperature so you need to make sure everything is within easy reach. You also must have just woken from at least three to four straight hours of sleep.

As your body goes through hormonal changes, your body temperature drops slightly right before the release of an egg. Then, 24 hours after the egg is released, your body temperature rises and stays slightly elevated for a few days. The temperature changes are so small – often less than a ½ degree – that you might need a special thermometer to accurately measure the temperature changes.

What you are looking for is the rise in your body temperature. The two to three days before your temperature increases are your most fertile days and the days you have an increased chance of conceiving. You will look for the same rise the following month to get an idea of which days of the month are the best time to have unprotected sex.

You should find a fertility tracking calendar that is easy to use and consistently track your temperature throughout your whole cycle. It will take a few months of tracking your temperature before you can start to see a pattern. But by tracking your basal body temperature over time you will be able to make an educated guess of when your fertile days fall each month.


While BBT is an easy method to use it isn’t always the most accurate. With an accuracy of 76 to 88 percent it can be one of the less reliable methods of fertility tracking. Part of the reason it can be hard to use is because your basal body temperature is affected by much more than your hormonal changes. Your body temperature can be affected by many lifestyle and environmental factors including:

  • Interrupted sleep cycles
  • Stress
  • Illness
  • Certain medications
  • Alcohol intake
  • Travel and changes in normal schedule

For the most accurate results you also need to take your temperature at the same time each morning. This method requires dedication and forethought to accurately use.

Irregular cycles can also make it difficult to use this method for accurate fertility tracking. If you experience irregular cycles it is best to discuss the use of this method with your doctor.

Since several studies have found that BBT can be inaccurate, it is best to use it in conjunction with another fertile awareness method such as cervical mucus, ovulation calculators, ovulation predictor kits.

Using Mira as well

Mira is a non-invasive way to monitor your fertility and plan for conception. It can be used in conjunction with other methods such as BBT to get a more accurate picture of your personal cycle. With a 99% accuracy for predicting ovulation you have a much better chance of timing intercourse to successfully conceive.

Basal body temperature doesn’t give you much warning of your fertile window. However, an OPK such as Mira can track your hormonal changes and give you warning that your fertile window is approaching. By using laboratory grade testing, Mira can accurately measure your full cycle even if your cycle changes month to month.

If you are trying to conceive you are probably stressed and might not be sleeping well. Take into consideration that these factors could affect the accuracy of your BBT results. If you cannot accurately predict which days to have sex for conception your chances of pregancy decrease.

The body temperature method can only tell you once you have already ovulated so you have to set aside a few months to diligently track your basal temperature before you can use it for family planning. If you are looking to use data right away to start trying to conceive the BBT method isn’t going to provide that.

In your journey to conceiving it is best to discuss different methods with your healthcare team to get information about accuracy and steps for proper usage. Using several methods together can provide peace of mind that you are giving yourself every chance to successfully conceive as quickly as possible.

If a method such as BBT doesn’t fit well into your lifestyle or causes stress don’t feel like you have to use it. There are many methods of fertility awareness available and finding the one that fits your lifestyle is going to make what can be a stressful journey a little easier.

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