Ovulation and temperature: How to detect and what’s normal
Lauren McKay
Dr. Danielle Perro
Follows NC° Editorial Policy
At Natural Cycles, our mission is to empower you with the knowledge you need to take charge of your health. At Cycle Matters, we create fact-checked, expert-written content that tackles these topics in a compassionate and accessible way. Read more...
Key takeaways:
- Temperature and ovulation are linked – and tracking your basal body temperature can be a good way of better understanding your menstrual cycle
- Basal body temperature is your body’s lowest resting temperature, and it can give insights into your fertile window
- Tracking your basal body temperature can help you predict when you’re ovulating – useful whether you’re trying to get pregnant or want to avoid pregnancy
In this article, we’ll take a deep dive into the relationship between ovulation and temperature, both in relation to traditional fertility awareness methods and newer technology. We’ll look at how different approaches measure body temperature. We’ll look at the link between your body’s temperature and the menstrual cycle, how basal body temperature changes around ovulation, and how tracking basal body temperature can help you either prevent or plan pregnancy. Read on to find out more about this natural method, whether you’re looking to get pregnant or avoid pregnancy.
Temperature and ovulation
Did you know there’s a link between the menstrual cycle and your body temperature? Basal body temperature (BBT) is the body’s lowest resting temperature, which is typically measured first thing in the morning before you get up. A change in hormones around ovulation causes this to rise [1]. Measuring basal body temperature to identify when you ovulate 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 when you’re ovulating, so relying on calendar dates alone to know where you are in your cycle doesn’t provide the full picture.
How can you predict when you will ovulate?
Your basal body temperature can help you to better understand your menstrual cycle – so keeping track of your temperature can give you an idea of when you’ll ovulate.
Before you’re ovulating, a your average basal body temperature is between 96°F (35.5°C) and 98°F (36.6°C). After ovulation, there’s a slight increase in average BBT to between 97°F (36.1°C) and 99°F (37.2°C) [2]. If you become pregnant, this temperature rise will remain higher. However, if you’re not pregnant, it will drop again, prompting the start of your period, and so a new cycle begins.
Why measure basal body temperature?
It might sound strange to take your temperature when you’re feeling healthy. But measuring basal body temperature is a great way to help you predict ovulation. In other words, BBT is key to fertility awareness-based methods of family planning.
Fertility awareness is all about understanding when you’re most fertile in your menstrual cycle and on what days you can get pregnant. By tracking your basal body temperature every day, after a few months, you’ll have a better idea of when you’re ovulating and when you might get your next period – useful whether you’re trying to avoid pregnancy or want to conceive. If you’re trying for a baby, that means you know which days you’re most likely to conceive, and can plan sex accordingly – and if you’re avoiding pregnancy, it means you’ll know which days you should use additional protection like condoms or abstain from sex.
There are other fertility awareness-based methods of family planning, including counting cycle days, tracking cervical mucus, and taking ovulation (LH) tests – but counting cycle days does not account for variation like shifting ovulation, and interpretation of cervical mucus can be challenging. On the other hand, measuring BBT can show a definite rise in temperature, confirming that ovulation happened [3].
Tracking your BBT can also help you detect pregnancy before you even take a test. After ovulation, your basal body temperature rises due to the release of progesterone. If you become pregnant, progesterone will continue to be released to help the fetus develop, meaning your temperature will remain elevated [1].
Pros of measuring basal body temperature
Education: Everyone’s body and cycle are different, which is why basal body temperature tracking can be so valuable. It helps you to really get to know what’s normal for you, and tracking your basal body temperature over multiple cycles can help you to spot trends in your cycle length, timing of ovulation, and the duration of your luteal phase.
Sharing with doctors: All of that information can be useful not only for getting to know your body better, but also for sharing with a doctor if you ever need to. BBT tracking can help to confirm whether you’re ovulating during your menstrual cycle [1], which you can’t know from having periods alone. This can help you to identify any potential fertility issues early, such as anovulatory cycles where no egg is released [4].
Plan or prevent pregnancy: Measuring BBT can give you a deeper understanding of when you’re most fertile during your cycle. That means you can make more informed decisions about when to have unprotected sex, depending on your goal.
Hormone-free: Basal body temperature tracking is hormone-free. That means it’s suitable for people who can’t or don’t want to take hormonal birth control due to medical reasons, side effects, or personal preferences.
Cons of measuring basal body temperature
Manual work: If you choose to measure BBT and chart it yourself, it can be a large undertaking, and is significantly more work than other methods used to prevent pregnancy (like taking a birth control pill).
Open to human error: If you are recording the data yourself, and using this method for something as important as finding your fertile window, it’s important to note that a miscalculation or a mistake in the data can have consequences
Might not be suitable for irregular cycles: If your cycle length tends to change a lot then measuring BBT can become more tricky as you may have to do additional calculations or be more cautious when it comes to determining the fertile window [5].
No protection from STIs: If you choose to use the BBT method as your main contraceptive, keep in mind that it can’t protect you from sexually transmitted infections. If you are at risk of these, it may be a good idea to consider barrier methods, like condoms, which can be used instead of or in addition to fertility awareness methods..
Not highly effective as birth control: While using BBT as a contraceptive can be a great option for some, it’s worth noting that there are other, more effective methods out there. Long-acting methods such as the copper IUD, the hormonal IUD, and the implant are all more than 99% effective at preventing pregnancy [6].
Natural Cycles vs. the BBT MethodThis article focuses primarily on the biology of the cycle and traditional basal body temperature methods. However, Natural Cycles, the first FDA Cleared birth control app, does share similarities with these types of fertility awareness-based methods. The Natural Cycles algorithm processes body temperature along with information about your period and optional LH tests to generate a fertility status, which you can access each day via the app. You can choose to measure using a BBT thermometer, or with a wearable device such as an Oura Ring or Apple Watch. Unlike traditional BBT, no trial period is needed — Natural Cycles is effective from day one. And because the algorithm does the hard work for you, no manual calculation is needed. Natural Cycles is 93% effective with typical use and 98% effective with perfect use. We’ll cover how Natural Cycles works in more detail later in this article… |
How to measure basal body temperature
To measure your temperature in this way, you will need a basal body thermometer. This is a specific kind of digital thermometer that shows two decimal places. You can usually find these at the pharmacy or you can also order BBT thermometers online (or get yours for free when you sign up for Natural Cycles annual plan).
To get the most accurate results from tracking your BBT, there are a few things you should keep in mind:
- Take your basal body temperature first thing in the morning before you sit up, or get out of bed. This is because you need to measure the body’s lowest resting temperature.
- Remember to measure your basal body temperature using your basal thermometer at around the same time every morning. You can set an alarm clock if it helps you to remember.
- Track your BBT regularly. It’s recommended that you check your fertility markers – including your body temperature and changes to your cervix – every day [7].
- Watch out for sleepless nights: It’s best to get at least three hours of uninterrupted sleep for a more accurate reading. If you had a bad night’s sleep, you can skip measuring the next day.
- Make sure to record any notes about irregularities, such as if you’ve had less sleep, are hungover, or are taking any new medications.
How hormones affect temperature
You might be wondering what causes this mysterious temperature shift throughout your cycle...well, it’s all about hormones! Let’s take a closer look at how these change throughout the cycle.
Does your body temperature rise before your period?
There is fluctuation in your body temperature throughout your menstrual cycle, and it’s usually slightly increased in the luteal phase [8]. Or, in other words, your basal body temperature does rise during the part of your menstrual cycle that begins after ovulation and ends the day before your period starts.
Hormones during your cycle and their impact on basal body temperature
During the first half of your cycle, the main sex hormone present is estrogen [9]. This hormone is associated with the things that make us feel good when we’re ovulating and the days leading up to getting our period, i.e., better mood [10], high sex drive [11], and clear skin [12]. However, it's the luteinizing hormone (LH) that’s responsible for triggering ovulation itself [13].
Right before ovulation, progesterone levels also start to rise. After ovulation, estrogen levels drop off, while progesterone hormone levels stay high for the latter part of the menstrual cycle [9]. Progesterone not only causes symptoms commonly associated with premenstrual syndrome (PMS), such as sluggishness and irritability [14], but it’s also what causes body temperature to rise and stay high [8].
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 [15]. While you’ll see a dip in temperature before your period begins, as mentioned earlier, those who are pregnant may notice their temperature stays higher due to the presence of this hormone [1].
Hot flashes before your period
If you’ve ever had hot flashes before your period, you’re not alone. While hot flashes are more commonly associated with being a symptom of perimenopause, it’s been found that around 10% of women with anovulatory periods get hot flashes [16].
It’s thought that this is down to the drop in estrogen levels before your period, which may affect the hypothalamus (the part of your brain that’s responsible for keeping your body at a stable temperature) [17].
If you experience hot flashes before your period, wearing layers (so you can remove a shirt or sweater if you’re feeling hot), using a fan – if you’re out and about, a handheld fan is a good idea – and drinking cool drinks can help to manage these symptoms.
How daily basal body temperature charting can help you track your cycle
Tracking your basal body temperature helps you to understand if and when you’re ovulating. When your ovaries release an egg, there is also an increase in progesterone production, and your basal body temperature rises – usually by between 0.5 to 1.0 degrees Fahrenheit [1].
Phase 1: Follicular
Your basal body temperature usually drops before ovulation and then rises. During the follicular phase of your menstrual cycle (the first phase of the menstrual cycle, which starts with your period and ends with ovulation), your basal body temperature tends to stay quite low. It will usually be between 96 and 98 degrees Fahrenheit during this phase, until just before ovulation, when there will be a significant drop in BBT.
Phase 2: Luteal
During the luteal phase (the second phase of your menstrual cycle, which takes place after ovulation and before your period), your basal body temperature rises by 0.5 – 1 degrees Fahrenheit. That’s because during the luteal phase, the corpus luteum starts to secrete progesterone – and as progesterone levels start to decrease, your basal body temperature will return to normal a day or two before your period starts [18]. If it remains elevated when your period is due, it is possible that you are pregnant – this is a good time to take a pregnancy test.
When can you safely have sex using the basal body temperature method?
When tracking your body temperature, it’s considered that your ‘safe days’ begin once you’ve had at least three consecutive days at an elevated temperature. This lasts until your temperature drops just before your next period [2].
If you’re using Natural Cycles, then you’ll already know which days you can have sex without getting pregnant. These are shown in your app as Red Days (not fertile), and include the fertile window and an extra buffer to allow for irregular cycles, or ovulation moving.
Remember, too, that barrier methods like condoms are the only way to protect against sexually transmitted infections, so if you’re at risk of STIs, you may want to use these as an extra method of contraception with any other method of birth control.
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 or drinking alcohol
- Sleeping significantly more or less than usual
- Some thyroid conditions
- Menopause
- Working shifts where your sleep cycles may be affected
- Environmental factors like the temperature [2]
If you measure basal body temperature with NC°, the app’s algorithm is able to detect changes in temperature and can exclude a reading if it is higher or lower than usual.
Key things to remember when using the basal body temperature method
Basal body temperature tracking is simple in principle – but there are a few things to remember to ensure you get the most out of the basal body temperature method, whether you want to get pregnant or avoid it. For the most accurate results:
- Use your BBT chart to better understand your cycle, when you ovulate, and when you can get pregnant.
- Use your fertility status to plan when to have sex if you’re trying to get pregnant, or when to abstain (or use another method of protection).
- Remember that other factors can affect your basal body temperature, such as if you measure it at a different time of day, if you’re on medication, or if you’re suffering from insomnia.
How to measure basal body temperature with Natural Cycles
Natural Cycles works a little differently to traditional basal body temperature methods. There are two ways of measuring your temperature with Natural Cycles:
- Using an NC° thermometer when you wake up (to measure your basal body temperature)
- Using an Oura Ring or Apple Watch while you sleep (to measure your skin temperature)
Our algorithm uses this data to learn your unique menstrual cycle and determines when your most fertile days are.
While old-school basal body temperature charting methods can require a lot of time and are difficult to use, NC° 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.
To use Natural Cycles, you should:
- Take your temperature most mornings when you wake up. We recommend aiming to measure (temperature) at least five times a week. This ensures that the algorithm has plenty of data to give you the most accurate results to narrow down your fertile window. The effectiveness won’t change if you add less data, but your fertile window will get bigger.
- Input the temperature reading into the NC° app.
- Get your daily fertility status: The app will then use your data to calculate your fertility status for the day and tell you whether or not you are fertile. This is displayed as either green (not fertile) or red (use protection) in the app.
Unlike basal body temperature tracking, you can still use Natural Cycles if you have an irregular period, an underactive thyroid, or a condition that can affect your temperature. It just means that you may be given more Red (fertile) Days per cycle if the app cannot identify your ovulation day. However, this does not make it any less effective – it simply means that you would be given a ‘buffer’ with more Red Days than the fertile window.
If you’re using Natural Cycles as a birth control method, you must use protection or abstain from sex on fertile days. It’s 100% hormone-free and is 93% effective at preventing pregnancy with typical use and 98% effective with perfect use. (Using the app perfectly means never having unprotected sex on Red Days.) Natural Cycles is not suitable for those under 18 years of age and does not protect against STIs.
Choose your fertility goal
Natural Cycles was FDA Cleared in the US back in 2018. It offers a hormone-free option for women who also want to learn more about their bodies. It's designed to be more accurate and easier to use than traditional fertility awareness-based methods. While Natural Cycles can be used as birth control to prevent pregnancy, it can also be used as natural family planning 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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