Trying to figure out when you’re most fertile? The basal body temperature method—an age-old fertility awareness method involving taking your temperature during a resting state—can help you determine the best days to have sex if want to get pregnant, or, just the opposite, the best days to avoid having sex in order to not get pregnant!

Sounds simple, right? It is… once you master the basics. Read on to find out:

  • What basal body temperature is
  • How to take and chart basal body temperature
  • How effective tracking your basal body temperature method is
  • Plus, what your basal body temperature means

What Is Basal Body Temperature?

The Basal Body Temperature is the body’s lowest temperature at rest. It is measured by taking your temperature immediately upon awakening and is only accurate if very minimal movement has occurred.

Charting the ever-so-slight changes in your Basal Body Temperature that occur during ovulation and/or pregnancy is a type of natural family planning, or fertility awareness method.

How does basal body temperature do all that?!

When you ovulate, the hormone progesterone causes your temperature to rise. This slight temperature rise will stay elevated for approximately two weeks. Then, just before your period starts, the hormone progesterone drops, and your basal body temperature will drop too—but, if you become pregnant, your temperatures will remain higher because progesterone will stay high to sustain your pregnancy.

In the chart below, you’ll see that this woman ovulated on day 16, when her temperature spiked. With this information, she can gather that she’d be most fertile on days 10 through 17. Since she had sex five times within this window (as seen by the circle around the day), her chance of getting pregnant is good.

Why Use Basal Body Temperature for Family Planning?

If you’ve ever thought about birth control and fertility, you know it’s a complicated topic. Though some women use conventional birth control options out of convenience or necessity, methods like the pill do have proven health risks, such as heart attack, stroke, or blot clots. (source)

Learning how to chart your basal body temperature, combined with awareness of other signs of fertility (cervical discharge and cervical position for example), is an effective and non-invasive approach to birth control.

Putting together the basal body temperature method plus watching for other signs of fertility is called the Symptothermal Method.

To break it down even further, the ‘‘Sympto’’ part stands for:

  • Increase in cervical fluid, which changes in amount and consistency, becoming stretchy and similar to egg-yolk when fertile

And the “ Thermal” part stands for:

  • Basal body temperature, which rises after a woman ovulates (when the ovary releases an egg) and drops when your period begins

Research shows that both a rise in temperature and fertile mucus are reliable signs of fertility, and when present together, is the most likely time to become pregnant.

How Effective Is Tracking Your Basal Body Temperature?

If used correctly and consistently, one study suggests basal body temperature monitoring is 99.6 percent effective.

But it’s important to note that this statistic is based on proper use. Basal body temperature can be influenced by many factors, including:

  • Illness or fever
  • Stress
  • Shift work
  • Interrupted sleep cycles, such as getting up to urinate several times during the night, or oversleeping
  • Alcohol
  • Travel and time zone differences
  • Gynecologic disorders
  • Certain medications
  • Some women also ovulate without a clear rise in basal body temperature

Charting your basal body temperature can be a tricky skill to master, even just getting up to go pee, or rolling over several times in bed before taking your temperature can affect the reading. Consistency and dedication is key! Some moms like to combine BBT tracking with other non-invasive devices to ensure accuracy.

How to Take Basal Body Temperature

In most women, basal body temperature will go up at least four-tenths of a degree (usually more like 1/2 a degree) for at least 3 consecutive days after ovulation. In order to effectively measure your BBT, follow these simple steps closely:

  1. Each night, set your thermometer by your bedside.
  2. Take your temperature at the same time each morning, or with no more than a 30-minute time difference.
  3. When you get up, immediately reach for the thermometer and take your temperature either orally or under your armpit. Let the thermometer stay in your mouth for up to five minutes to be sure you have your true temperature.
  4. Do not get up to go to the bathroom or have a sip of water or even move before you take your temperature—this can throw off results.
  5. If you’re breastfeeding in the night or get up to pee, be sure that you have four consecutive hours of sleep before you take your temperature.
  6. It is important to use the same thermometer for the entire menstrual cycle. If you purchase a new thermometer, consider waiting until the first day of your next cycle to start using it.

Charting Your Basal Body Temperature

In order to start tracking your daily basal body temperature, you will need a good chart. You can certainly make your own, but there are many available online as well. Some women prefer to use a mobile app to help them keep track of their basal body temperature.

No matter the method, it’s important to chart your temperature reading daily in order to watch for patterns.

Once you’ve established a charting system, start your temperature readings and charting on the first day of your period.

Along with temperature, here are few other things you might want to keep track of in your charting:

  • The time of day you took your temp
  • The days that you have sex
  • Illnesses, stressors, travels, difficulty sleeping, alcohol consumption, late night
  • Cervical mucus
  • Cervical position (high or low)

Can You Take Your Basal Body Temperature With a Normal Thermometer?

Yes, but it’s not as accurate. For best results with this method, buy a thermometer specifically meant to track BBT.

There are many styles of digital thermometers on the market (where to buy) that are specifically designed for taking your BBT. Prices range from $14 to $40.

If you want a more sophisticated tool to measure temperatures, you could purchase a Lady-Comp Fertility Monitor. While it is definitely pricey, the company stands behind a 99.3% accuracy rate and customers stand behind its effectiveness. And if you think of it, the price can be cheaper than the other methods over the long-term.

What Is a Normal Basal Body Temperature?

Your body temperature goes through slight temperature changes throughout your menstrual cycle. It is lower in the first part of your cycle and then rises when you ovulate. For most women, the basal body temperature in the days before ovulation is between 96 to 98 ℉. After you ovulate, it goes up to 97 to 99 ℉.

If you find that your temperature is much lower than expected, you may want to check in with your healthcare provider. Low BBT could indicate a change in hormone levels, hypothyroid, or fatigue.

What Is Your Basal Body Temperature When You’re Ovulating?

Once ovulation occurs, the basal body temperature stays slightly elevated, somewhere between 97 to 99 ℉.

Your most fertile days are about two days before your BBT rises. Sperm can live in the body for 2 to 3 days, so if you are hoping to get pregnant, this is the best time to have sex.

What Is Your Basal Body Temperature When Pregnant?

A rise in basal body temperature that lasts for 18 or more days may be an early sign of pregnancy.

The rise is typically less than a half a degree, but as you get to know your basal body temperatures you will be able to detect a rise and a trend in your own body temperatures. This elevation is usually between 97 to 99 ℉.

Remember…

Basal body temperature charting is just one piece of the puzzle when trying to understand your fertility signs. If you choose to use this method for family planning, you will have to be diligent and consistent. It’s actually kind of fun to do this and to really get to know your body in these subtle ways. If you need help to boost your fertility, check out these tips and always work with a doctor to get to the root issues. Now, go forth and be empowered, mama!

How About You?

Have you ever tried the Basal Body Temperature Method to track fertility? Did you find it effective? What do you think?