Ovulation Temperature: How to Measure BBT

In this post, we’ll look at the link between temperature and the menstrual cycle, how basal body temperature changes around ovulation, and how measuring your temperature can help you either prevent or plan pregnancy. Read on to find out more...

Red temperature linechart on pink background with ovulation marked. The word 'Hormones' is written in white text and 'Basal Body temperature' in red.

Temperature and ovulation

Did you know there’s a link between the menstrual cycle and your body temperature? Basal body temperature (also known as BBT) is the body’s lowest resting temperature. A change in hormones around ovulation causes this to rise. Measuring BBT to identify ovulation gives you unique insights into your fertile window, in turn giving you increased control over your fertility. There are many things that can affect the timing of ovulation, so relying on calendar dates to know where you are in your cycle may not be as exact. 

Why measure BBT?

Measuring your temperature when you’re feeling healthy may sound strange. However, measuring BBT is the most reliable way to confirm where you are in your cycle. Other methods such as counting cycle days, tracking cervical mucus, or taking ovulation tests can only give an indication of when ovulation may happen, whereas measuring BBT can show a definite rise in temperature after it’s happened. 

How to measure BBT

To measure BBT you need a basal body thermometer. This is a specific kind of thermometer that shows two decimal places. You can usually find these at the pharmacy, you can also order BBT thermometers online, or you can get one for free when you sign up for a Natural Cycles annual subscription

Once you have your BBT thermometer, you need to measure your temperature first thing in the morning before you get up and out of bed. This is because you need to measure the body’s lowest resting temperature. At Natural Cycles, we recommend aiming to measure at least five times a week. 

What’s a normal ovulation temperature?

Before ovulation, a woman's average resting temperature is between 97°F (36.1°C) and 97.5°F (36.4°C). After ovulation, average BBT increases to between 97.6°F (36.4°C) and 98.6°F (37°C). If a woman is pregnant, this temperature rise will stay high. However, if a woman isn’t pregnant, it will drop again, causing her to get her period, and so a new cycle begins. 

How hormones affect temperature

You might be wondering what causes this mysterious temperature shift...well, it’s all about hormones! During the first half of your cycle, the main sex hormone present is estrogen. This hormone is associated with the things that make us feel good around ovulation i.e. increased energy levels, high sex drive and clear skin. However, it's the luteinizing hormone (LH) that’s responsible for triggering ovulation itself. 

Right before ovulation, progesterone levels also start to rise. After ovulation, estrogen levels drop off. However, levels of the hormone progesterone stay high for the latter part of the menstrual cycle. Progesterone not only causes symptoms commonly associated with PMS, such as sluggishness and irritability, but it’s also what causes body temperature to stay high. 

Progesterone is an important hormone in early pregnancy as it helps with the implantation of a fertilized female egg cell and helps get the body ready for pregnancy. While you’ll see a dip in temperature before you get your period, those who are pregnant may notice their temperature stays higher due to the presence of this hormone.

How to measure BBT with Natural Cycles

Natural Cycles is an app that uses the basal body temperature method paired with an algorithm that learns your unique menstrual cycle. While old school charting methods can require a lot of time and difficult to use, Natural Cycles is designed to be user-friendly. It also offers greater accuracy than traditional fertility awareness-based methods, such as the rhythm method and other calendar-based methods. 

Take your temperature most mornings when you wake up. Input the temperature reading into the Natural Cycles app. The app will then use your data to calculate your fertility status for the day and tell you whether or not you are fertile. You can use Natural Cycles as a birth control method or to plan pregnancy

If you’re using Natural Cycles as a birth control method, you must use protection or abstain from sex on fertile days. Natural Cycles is 100% hormone-free and is 93% effective at preventing pregnancy with typical use and 98% effective with perfect use.

Other than ovulation, what can affect resting body temperature?

Our bodies are living, breathing, organic things so of course they don’t always operate like clockwork! There are a few things that can affect our basal body temperature. These include:

  • Being unwell
  • Being hungover
  • Sleeping significantly more or less than usual
  • Some thyroid conditions
  • Menopause

If you measure BBT with Natural Cycles, the app is able to detect changes in temperature and can exclude a reading if it is higher or lower than usual. If you have an underactive thyroid, or are going through menopause, you can still use Natural Cycles, just be aware that you might get given more red (fertile) days per cycle if the app cannot identify your ovulation day - this does not make it any less effective. 

Choose your fertility goal

Natural Cycles was cleared for use as birth control by the US FDA back in 2018. It offers a hormone-free option for women who also want to learn more about their bodies. While Natural Cycles can be used as birth control, it can also be used to plan pregnancy if and when you’re ready to start a family. Are you ready to start your hormone-free journey?

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Written By

Jennifer Gray

A writer with a passion for women’s health, Jennifer Gray has years of experience writing about various reproductive health topics including birth control, planning pregnancy, women’s anatomy, and so much more.

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Scientifically Reviewed

Jack Pearson

With 10 years of experience working in the field of fertility, Jack Pearson is Natural Cycles’ in-house expert. As Medical Affairs Manager, he dedicates his time to conducting groundbreaking research and educating healthcare professionals.

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