Basal body temperature: Why track it if I want to get pregnant?

Jul 11, 2023

Basal body temperature is the body’s temperature while resting. During ovulation, BBT rises slightly. Tracking BBT over several months can help a person predict when they will ovulate and be most likely to get pregnant.

A female is most likely to get pregnant 2–3 days before ovulation, on the day it occurs, and 12–24 hours afterward.

If a person wants to conceive, they can track their BBT for a few months to understand when ovulation usually occurs within their menstrual cycle. A person can plan to have sex during their most fertile period to increase the likelihood of getting pregnant.

This article explains what BBT is and the reasons to track it. It also discusses a female’s most fertile period and how to predict it using the BBT method.

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

BBT is the lowest body temperature that occurs after rest. In most people, a change of 0.5–1F° will occur following ovulation.

If a person wants to use the BBT method of temperature charting, they should measure their temperature at the same time every day, first thing after waking up. It is important to take the temperature before getting out of bed, eating, drinking, having sex, or doing anything else.

There are around 6 days each month when a female can conceive. If a person is trying to get pregnant, it can be helpful to know when they are ovulating.

BBT is usually lower on the days leading up to ovulation. After ovulation, it will rise again within 24 hours and remain raised.

A person can record their daily readings on a chart to make differences easy to detect. The temperature changes are very slight, so a thermometer that measures to at least tenths of a degree is the most accurate method.

Learn more about ovulation here.

A person’s menstrual cycle begins on the first day of menstruation and typically lasts around 28 days, although this can vary between 21–40 days.

Ovulation occurs about 2 weeks before the start of menstruation, midway through a person’s cycle. A person is most likely to conceive on the day of ovulation, 2–3 days before, or 12–24 hours afterward. This is around days 10–16 of the menstrual cycle.

A male’s sperm can live for 3–5 days in a female’s reproductive tract. If a female has sex with a male without using a barrier method a few days before ovulation, the sperm can fertilize the egg, and they can become pregnant.

Once ovulation occurs and the ovary releases an egg, it has 12–24 hours for sperm to fertilize it before it dies or the body reabsorbs it. After this time, pregnancy is less likely to occur until the next menstrual cycle.

Learn more about conception here.

For most women, 97–98°F (36.1–36.6°C) is a typical BBT before ovulation. After an ovary releases an egg, BBT rises.

During ovulation, BBT will rise by 0.5–1°F on average to 97–98°F (36.1–36.6°C) and remain higher until the end of the menstrual cycle. A female’s most fertile days are 2–3 days before BBT rises.

By tracking their BBT over several months, a person can identify patterns that will help them predict when they will ovulate and optimize their chance of conceiving.

It may be challenging to interpret a BBT chart at first. A medical professional or family planning clinic can help with this.

The BBT method is not completely reliable for the following reasons:

External factors can influence BBT readings, including:

A person should measure their body temperature first thing every morning when they wake up — before eating, drinking, having sex, or any other activity.

To measure BBT, a person can use a digital or BBT thermometer that measures in tenths of a degree.

A person can record each day’s reading on a chart. This can be on paper, an app, or online. Once a person has tracked a few months of BBT readings, they can study the pattern to identify the time in the cycle when their BBT rises.

A rise in BBT indicates that ovulation has already occurred, so a person can try to time sex on the days before the temperature rise occurs for the best chances of getting pregnant.

Taking a BBT requires a thermometer that measures to tenths or hundredths of a degree. Many are available as digital thermometers, or a person can buy a special BBT thermometer.

Below are examples of thermometers:

BBT is the lowest temperature that occurs after rest. During ovulation, a female’s BBT rises slightly.

Tracking BBT over several months can indicate when ovulation usually occurs within a person’s menstrual cycle. If an individual wants to get pregnant, they can plan to have sex during their most fertile days.

External factors can affect BBT, such as drinking alcohol, smoking, illness, or not taking a BBT reading immediately upon waking.

To take BBT readings, a person can use a digital thermometer that measures to tenths or hundredths of a degree.