Basal Body Temperature Test

Overview

The basal body temperature (BBT) method is a natural way to track fertility. BBT refers to a person’s lowest resting temperature, usually measured immediately after waking. During the menstrual cycle, a slight increase in BBT typically occurs around ovulation. Daily monitoring helps predict when ovulation is likely.

BBT usually rises by about 0.5 to 1°F (0.3 to 0.6°C) after ovulation. The most fertile days are typically the two to three days before this temperature increase. Many individuals use the BBT method to plan pregnancies. Some use it to identify the best days for intercourse, while others rely on it to avoid unprotected sex when trying not to conceive.

Benefit	Limitation
Non-hormonal	May not give enough time to prevent pregnancy
Inexpensive	Often paired with other methods

This method is often more effective when combined with other fertility awareness strategies.

Reasons for Using This Method

Many people track BBT to understand fertility or manage birth control. It’s a key part of natural family planning, helping to identify the most likely days for conception or pregnancy prevention. Some choose this method for personal or religious reasons, since it doesn’t involve hormones or devices. It has no side effects and is low-cost, requiring only a thermometer and a way to record data.

BBT tracking may also help detect early pregnancy. If the temperature remains elevated for more than 18 days after ovulation, this may indicate pregnancy. People often combine this method with cervical mucus tracking or fertility monitors. These approaches—symptothermal or symptohormonal methods—provide more precise ovulation insight.

Benefits

• No hormones or chemicals
• Fits with religious beliefs for some
• Cost-effective
• Can support use of barrier contraception

Common Uses

Purpose	Description
Fertility tracking	Finding best days to conceive
Birth control	Avoiding pregnancy naturally
Pregnancy detection	Spotting early signs

Possible Drawbacks

The BBT method doesn’t cause side effects or physical harm, but has limitations. It doesn’t protect against sexually transmitted infections (STIs) and is less reliable than other birth control methods. For example, around 1 in 4 women using fertility awareness may become pregnant within a year of typical use.

Consistent, careful tracking is crucial. Stress, travel, sleep issues, and illness can affect readings. To prevent pregnancy, couples should either abstain or use another method during fertile days. Some find daily recording difficult or stressful over time.

Main Risks	Details
Pregnancy	Higher chance compared to other methods.
Infections	No protection from STIs.
Stress Factors	Tracking can feel stressful.

How You Prepare

Getting started is simple. No special equipment is needed, though a digital thermometer with two decimal places works best. Consult a healthcare provider if you’ve recently had a baby, stopped hormonal birth control, are breastfeeding, or nearing menopause.

Interference	Examples
Health	Illness, fever
Lifestyle	Stress, alcohol, travel, shift work, changes in sleep patterns
Medical	Some medications, certain disorders

What You Can Expect

When you use basal body temperature for fertility awareness, take your temperature every morning before getting out of bed. You get the most accurate results when you use the same thermometer, take your temperature at the same time daily, and have at least three hours of rest beforehand.

Record temperature readings on paper charts or in an app. Over time, a pattern appears. Before ovulation, basal body temperature is usually around 97–98°F (36.1–36.7°C). When ovulation happens, a slight increase—usually about 0.5°F (0.3°C)—shows up. This higher temperature tends to stay steady for at least three days.

Common Steps in Daily Monitoring:

• Use the same thermometer each morning.
• Record temperature at the same time each day.
• Make sure to have had enough sleep for accuracy.
• Mark each temperature on a chart or app.
• Look for a temperature rise that stays high for several days.

Fertility awareness methods, like the symptothermal method or Billings method, combine temperature monitoring with checking other signs such as cervical mucus. Cervical mucus often changes before ovulation, becoming clear and stretchy, which helps identify the most fertile days.

Couples tracking for conception should have sex during the most fertile days, which are about two days before the rise in temperature. Since sperm can live up to five days in the body, planning in advance is important. Those trying to avoid pregnancy should avoid unprotected sex from the start of a cycle until at least three to four days after the temperature increase.

Sign	What to Watch For
Basal Body Temperature	Small, lasting rise after ovulation.
Cervical Mucus	Becomes clear and stretchy near ovulation.
Fertility Window	Two days before, the temperature goes up.
Fertility Awareness Tracking	Combines observations for better results.

Interpreting BBT Results

Consistently checking your BBT each morning—after at least six hours of sleep and before getting out of bed—helps produce accurate results. A noticeable rise in temperature often signals that ovulation has occurred, which can aid in either planning or avoiding pregnancy.

Cycle Phase	Average Temperature
Before Ovulation	97.0°F–97.5°F
After Ovulation	97.6°F–98.6°F

Tracking these results over time reveals patterns in the menstrual cycle and identifies the fertile window.