Ovulation and temperature: find your fertility

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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. A change in hormone levels after ovulation causes this to rise. 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 to know where you are in your cycle may not be as exact.

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 woman's average basal body temperature is between 97°F (36.1°C) and 97.5°F (36.4°C). After ovulation, there’s a slight increase in average BBT to between 97.6°F (36.4°C) and 98.6°F (37°C). If a woman is pregnant, this temperature rise will remain higher. However, if a woman isn’t pregnant, it will drop again, causing her to get her menstrual 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 to 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 if you’re avoiding pregnancy, it means you’ll know which days you should use additional protection like condoms.

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 and interpretation of cervical mucus can be challenging, whereas measuring BBT can show a definite rise in temperature after it’s happened. 

Tracking your BBT can also help you to 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.

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, you can also order BBT thermometers online, or you can get one for free when you sign up for the NC° Annual Subscription. 

To get the most accurate results from tracking your BBT, there are a few things you should keep in mind:

1. 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. 
2. 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. If you’re using Natural Cycles, you can turn on notifications in the app to get daily reminders.
3. Track your BBT regularly. We recommend aiming to measure 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.
4. 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.
5. Make sure to record any notes about irregularities, such as if you’ve had less sleep, are hungover, or are taking any new medications. If you are using Natural Cycles, you can track this in the app and can choose to exclude your temperature if you’re not feeling 100%.

How hormones affect temperature

You might be wondering what causes this mysterious temperature shift throughout your cycle...well, it’s all about hormones!

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 post-ovulatory luteal phase. 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. This hormone is associated with the things that make us feel good when we’re ovulating and the days leading up to that point, i.e., increased energy levels, higher 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, while progesterone hormone levels stay high for the latter part of the menstrual cycle, before dropping off before your period arrives. A change in hormone levels at the end of the cycle is thought to be responsible for symptoms commonly associated with PMS, such as sluggishness and irritability. 

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 your period begins, those who are pregnant may notice their temperature stays higher due to the presence of this hormone.

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 menopause, it’s been found that around 1 in 10 women with regular periods get hot flashes.

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).

If you experience hot flashes before your period, it’s best to try to stay as cool as possible. Wearing layers can help (so you can remove a shirt or sweater if you’re feeling hot), so can using a fan – if you’re out and about, a handheld fan is a good idea – and drinking cool drinks.

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 Celsius. With some practice, you can start to understand your cycle. 

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 97 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. If it remains elevated when your period is due, this is a good time to take a pregnancy test.

When can you safely have sex using the basal body temperature method?

If you’re using NC° to track basal body temperature as a form of hormone-free birth control, you’ll therefore know that you need to plan sex carefully during the days that you’re most fertile. Your app will guide you with this, but generally, while you’re at your most fertile a couple of days before ovulation, due to potential sperm survival, there’s the potential that you’re fertile five days before ovulation. That means if you want to have sex during Red Days (your most fertile period), you’ll need to use a backup method of contraception like condoms. 

Remember, too, that barrier methods like condoms are the only way to protect against sexually transmitted infections, so you may want to use these as an alternative method of contraception alongside the app, depending on your circumstances.

If you’re trying to conceive, then your most fertile days are the best time for you to have sex.

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

If you measure basal body temperature with NC°, 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 NC°, 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.

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, you should:

• If you’re using Natural Cycles, enter the reading into your NC° app. You’ll then get your fertility status for the day. This is displayed as either green (not fertile) or red (use protection) in the app.
• 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 is an app that uses the basal body temperature method paired with an algorithm that learns your unique menstrual cycle. 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. 

Take your temperature most mornings when you wake up. Input the temperature reading into the NC° app. If you’re using it for family planning, 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 basal body temperature tracking as a birth control method to prevent pregnancy, or to plan pregnancy. 

We're constantly looking for new ways to improve the measuring experience for our Cyclers, and that also means offering more ways to measure. Instead of measuring orally with a thermometer, you can now measure overnight by wearing an Oura Ring or Apple Watch. These integrations work a bit differently from measuring with a thermometer since they measure throughout the night. However, Natural Cycles is just as effective when used with a wearable device. 

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.)

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?