BBT Explained: What Is Basal Body Temperature?

You might have heard about BBT or basal body temperature, but what do these terms actually mean? And, more importantly, why do they matter? Here at Natural Cycles, we’re on a mission to break down the language of science so every woman can understand her body a little better. So what is basal body temperature? Read on to find out….

Woman lying in bed with her eyes shut taking her temperature with a basal body thermometer

What is BBT?

BBT stands for either basal body temperature or basal body thermometer. These two things go hand-in-hand, or rather, thermometer-in-mouth, i.e. a basal body thermometer measures basal body temperature.

But what is basal body temperature you might well ask? Well, It’s more precise than normal body temperature which can be measured with a regular digital or mercury thermometer. Basal body temperature is the body’s lowest resting temperature which is best measured first thing in the morning, just after you’ve woken up. You need a specific thermometer to measure basal body temperature, this shows two decimal places.

Why measure basal body temperature?

Most people are used to measuring body temperature only when they are sick. In fact, there is a key link between fertility and body temperature. This is because right after ovulation happens in the menstrual cycle, there is a noticeable rise in basal body temperature. This slight, yet significant, shift cannot be picked up by a regular fever thermometer, so women who want to track their fertility use a basal body thermometer to identify their ovulation.

Once ovulation is identified through BBT, this information can be used to work out a woman’s fertile window. This info helps us understand our cycles better and with this knowledge we can do one of two things: plan a pregnancy, or prevent a pregnancy.

However, because every woman is different and her cycle is unique too, it’s not as simple as working out one ‘fertile window’ which applies to every woman. There are many other factors, such as period length and sperm survival, to take into account. This is why Natural Cycles, an intelligent app, is a popular birth control method for many women, and it can also be used to plan a pregnancy too. The app learns your unique fertile window and lets you know when you can and can’t get pregnant.

What else affects basal body temperature?

It’s not just ovulation that can cause a shift in BBT. If you haven’t had enough sleep, have a hangover, or are sick/on medication, all these factors can play a part in a rise of basal body temperature. If you are using Natural Cycles to track your cycle, then you will be able to add this info in the app as a ‘deviating temperature’.

Could a birth control app work for me?

If you are looking for a hormone-free method of birth control that teaches you about your unique cycle, then Natural Cycles could be the option you’ve been searching for. Natural Cycles requires you to measure your basal body temperature most morning (5 days a week) at the same time. Discover why thousands of women chose to switch birth control and have learned lots about their bodies along the way.

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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.