Basal Body Temperature

What is the basal body temperature method?

The basal body temperature (BBT) method helps determine when you’re most likely to get pregnant. Basal temperature is the temperature of your body when you’re completely at rest. Also called the temperature method, measuring your BBT is one way you can predict ovulation. Knowing when you ovulate (release an egg from your ovary) can help you identify the days you’re most likely to become pregnant. With this information, you can figure out when to have sex if you want to get pregnant or when to avoid sex if you don’t want to get pregnant.

How it works

Your body temperature rises slightly after ovulation. This is due to an increase in progesterone. Progesterone is a hormone responsible for preparing your uterus for pregnancy.

To use this method, you track your basal body temperature for at least three menstrual cycles. While you may not be able to predict exactly when you’re ovulating, measuring BBT may help you find a pattern. You can use this information to guess when you’re likely to ovulate. Depending on your goals for pregnancy, you’ll either have sex or avoid sex on the days before and just after ovulation.

What is the difference between body temperature and basal body temperature?

Your basal body temperature is your body’s temperature at complete rest or your lowest temperature. If you’re using the BBT method to chart your fertility, make sure to take your temperature before getting out of bed. Moving around, talking or even being awake for several minutes can affect your results.

You’ll also need a special basal thermometer. Basal thermometers show two decimal places. Normal thermometers may only show one decimal place. For example, 98.15 degrees Fahrenheit (36.72 degrees Celsius) instead of 98.1 F (36.7 C). You can find a BBT thermometer for about $10 at most drug stores.

Why is the basal body temperature method used?

People use this method to determine the fertile days of their menstrual cycle (or which days they’re more likely to get pregnant). Some people use BBT to identify the best days of the month to have sex because they want to get pregnant. People trying to avoid pregnancy may use it to know which days they should avoid having sex.

Some people choose the BBT method because:

• They don’t want to take medications or hormones.
• It’s inexpensive.
• There are no side effects.

It might take a while to get used to tracking and recording your temperature. Tracking other changes in your body like sore breasts or texture of your cervical mucus can also provide clues about when you’re ovulating.

How do I take my basal body temperature?

Start taking your basal body temperature on the first day of your period (the first day of bleeding). Continue to take it every morning until you get your next period. It may take several cycles to see a pattern. You’re looking for an increase in your body temperature, which means you’ve ovulated. Over time, you should notice your temperature increases around the same day each cycle. In a typical cycle, most people ovulate around day 14.

To use the basal body temperature method:

• Make sure you have a thermometer that measures temperatures to at least one-tenth (or two decimal places) of a degree. Look for a thermometer that says basal temperature on the packaging.
• Take your basal temperature as soon as you wake up. Keep your thermometer next to your bed. Take your temperature before you even stand up.
• Take your temperature at the same time. You should take your BBT at about the same time each morning. For example, if you wake up at 6 a.m. during the week, but sleep until 8 a.m. on weekends, your results won’t be as accurate.
• Measure your temperature from the same place every day. Most people measure BBT from their mouth, but you can also measure your temperature from your rectum (butt).
• Record your temperature each day. Use a graph or fertility-tracking app that allows you to compare each day’s temperature.
• Identify a temperature increase. Basal body temperature typically rises less than half of a degree Fahrenheit after ovulation. It may take a few cycles to determine when this rise occurs each month.
• Consider the fertile period. You’re most likely to get pregnant four days before and one day after ovulation.

What should my basal temperature be?

For most people, 96 to 98 F (35.5 to 36.6 C) is their typical temperature before ovulation. After you ovulate, it goes up to 97 to 99 F (36.1 to 37.2 C). How much it goes up is different for everyone, but it can rise as little as 0.4 F (0.22 C) or as high as 1 F (0.56 C).

Some people notice a slight dip in temperature just before ovulation. However, a sharp increase immediately follows this dip if you’ve ovulated.

Continue tracking after ovulation (until your period begins). If you’ve conceived that cycle, your BBT will stay elevated. That’s because your body needs progesterone for pregnancy. If you’re not pregnant, your temperature will drop and you’ll get your period a day or two later.

What is the basal temperature range when pregnant?

There isn’t a normal range, just what’s normal for you. If you’re pregnant, your temperature should stay elevated. You won’t see a drop in temperature just before your period. You should always get a pregnancy test or see a healthcare provider to confirm pregnancy.

Does basal body temperature rise before your period?

No, your basal body temperature drops before your period.

How do I know if I'm ovulating with the BBT method?

With the basal body temperature method, you won’t know you’ve ovulated until it’s already happening. That’s one drawback to the method. It’s also why you have to track your BBT for several menstrual cycles to identify what day ovulation typically happens for you.

When you’re interpreting your chart, remember to look for two distinct phases: before ovulation and after ovulation. Your temperature may be slightly different each day, but you should see a noticeable shift once you ovulate. When you see higher temperatures for at least three days in a row, you can assume you’ve ovulated.

Getting pregnant using BBT

If you’re using the basal body temperature method to get pregnant, tracking the days you’re most likely to ovulate is your goal. This helps you find a window of time that you’re most likely to get pregnant. For example, if you’re tracking your BBT and notice a temperature increase on days 12, 14 and 16, you’d probably want to make sure you’re having unprotected sex on days eight through 16 of your next cycle.

Remember, you can get pregnant up to four days before ovulation because sperm can survive in your uterus that long. That’s why the days leading up to ovulation are so important to identify.

What are the benefits of the basal body temperature method?

The basal body temperature method has no side effects and is highly affordable. The only cost is the price of the thermometer.

What are the drawbacks of the basal body temperature method?

The basal body temperature method isn’t accurate if you have irregular menstrual cycles or forget to take your temperature. It also offers no protection from sexually transmitted infections (STIs).

The BBT method isn’t very effective in preventing pregnancy because many factors can affect basal body temperature. If you don’t wish to get pregnant, most providers recommend using other forms of birth control in addition to taking your temperature.

Things that affect your basal body temperature include:

• Breastfeeding (chest feeding).
• Drinking alcoholic beverages.
• Fever caused by illness or infection.
• Not getting enough sleep.
• Stress.
• Taking some medications.
• Traveling to different time zones.

A note from Cleveland Clinic

Ask your healthcare provider if the basal body temperature method is right for you based on your desires for pregnancy. Charting your BBT is a natural and affordable way to track your menstrual cycle and predict ovulation. Many providers recommend combining the basal body temperature method with other fertility awareness methods if pregnancy is your goal. If you’re using BBT to avoid getting pregnant, using a second form of birth control increases your protection against pregnancy.