What is basal body temperature?

Your basal body temperature (BBT) is your lowest body temperature in a 24-hour period. It's the temperature of your body when you're at rest. Typically, BBT increases slightly right after you ovulate.

If you're trying to get pregnant, you can track your basal body temperature to estimate when you'll ovulate and determine the best days to have sex (or be inseminated). For greater accuracy, you can combine tracking your BBT with monitoring changes in your cervical mucus.

Keep in mind that your most fertile period is in the two to three days before the increase in BBT. So when you detect a temperature change, your optimal window for getting pregnant will likely have already passed. Nevertheless, if you have regular menstrual cycles and chart your BBT over time, this method may help you predict when you'll be most fertile.

Charting your BBT can also help your healthcare provider pinpoint the cause of any fertility problems.

How do I take my basal body temperature? Can I use a regular thermometer?

To get an accurate reading, you need to use a basal thermometer, which is sensitive enough to measure minute changes in body temperature. You can buy glass or digital BBT thermometers in your pharmacy or online. Although some digital ones give readings to a hundredth of a degree, all you really need is one that will give a reading to one-tenth of a degree (thermometers that only give readings to two-tenths of a degree are not accurate enough).

To get your BBT, take your temperature when you first wake up in the morning – before you eat, drink, have sex, or even sit up in bed or put a foot on the floor. Try to take a reading at about the same time each morning, and record it on a BBT chart (see below). If you don't take your temperature immediately after waking up, your BBT chart will not be accurate.

What is the normal basal body temperature?


You may notice your temperature occasionally spiking on other days, but if it doesn't stay up, you probably haven't ovulated yet.

Be aware that, in addition to ovulation, the following can also affect your BBT:

  • Pregnancy: If you become pregnant, your basal body temperature will stay elevated throughout your pregnancy.
  • Fever: Having a fever (if you get sick with the flu or another illness) will raise your overall body temperature, so your BBT won't be reliable.
  • Medications: Some medications, such as antibiotics or blood pressure medicines, can cause a rise in BBT.
  • Disease: Thyroid disorders can cause your body's temperature to increase.
  • Exertion or heat: Exercise and hot weather can push your temperature up.

What is cervical mucus?

Cervical mucus is vaginal discharge produced by the cervix. Over the course of your menstrual cycle, the amount, color, and texture of your cervical mucus changes due to fluctuating hormone levels.

Checking your cervical mucus and keeping track of these changes can help you tell when you're most fertile. Here's what to watch for:

  • Once your period stops, you may not have any discharge for a few days.
  • Then you may notice a few days of cloudy, sticky discharge.
  • In the few days leading up to ovulation, the amount of discharge increases and becomes thin, slippery, and stretchy (like egg whites). This consistency makes it easier for the sperm to travel through the cervix to the egg. These are your most fertile days.
  • Just after ovulation, the amount of mucus decreases and becomes thicker.
  • Then you may be dry for several days before your next period.

A good time to check your cervical mucus is when you go to the bathroom first thing in the morning, but you can check it any time of day. Sometimes you may be able to see cervical mucus on the toilet paper after you wipe. Other times you may need to insert a clean finger into your vagina (toward your cervix) to get enough mucus to examine.

Keep in mind that taking certain medications, having sex, using a lubricant, or douching can change the appearance of cervical mucus.

Ovulation charts: Tools for tracking your BBT and cervical mucus

This blank chart gives you a handy way to track your basal body temperature. You can also use it to track your cervical mucus. After charting your BBT for a few months, you'll be able to see whether there's a pattern to your cycle. If there is, you may be able to estimate when you'll next ovulate.

Print out some copies of our blank chart, buy a basal thermometer, and you're ready to start charting.

And if you want to see what a chart looks like when it's completed, take a look at our filled-in sample chart.

When you look at the sample chart, remember that every woman's cycle is different, and your personal chart may not look like the example or even be the same month to month.

How to chart your basal body temperature and cervical mucus

Ready to begin charting? Here's how to do it:

  1. On the first day you get your period, fill in the date and day of the week under cycle day 1. Continue noting the dates of your cycle until the first day of your next period.
  2. Each morning when you wake up – before you drink, eat, have sex, or even sit up in bed – take your temperature with a basal thermometer. Put a dot next to the temperature that matches your thermometer reading for that day. (You can also note the time you took your temperature. Try to take it at about the same time each morning.) Connect the dots to see how your basal temperature fluctuates from day to day.
  3. You can also check your cervical mucus each day if you wish. Record the type of discharge you find each day, according to the key at the bottom of the chart: P = period, D = dry, S = sticky, E = egg-white-like
  4. Toward the end of your cycle, watch for a day when your BBT rose 0.5 to 1 degree F and stayed high. That day is usually the day you ovulated. It should correspond with the last day you noticed egg-white-like cervical mucus. The days when you notice egg-white-like mucus are your most fertile.
  5. Track these symptoms for a few months to see if you notice an uptick in BBT and egg-white-like mucus at the same time each cycle. That will allow you to plan which days to have sex if you want to get pregnant.
  6. For the best chance of conceiving, have sex at least every other day during your most fertile period.

For more information, read about how to boost your chances of getting pregnant, connect with other couples trying to conceive, and learn the most common early signs of pregnancy.

What if charting doesn't work for me?

If the idea of charting sounds stressful, or if you just can't make it work, there are other ways to estimate when you'll ovulate. For example, you can try using an ovulation predictor kit, which measures your hormone levels and indicates when you're about to ovulate.

And if you have the flexibility to take a more low-key approach, you can just have sex about every other day during the middle two weeks of your cycle.

You can also try our ovulation calculator to figure out the dates you're most likely to be fertile.

Learn more

Ovulation predictor kits vs. charting: Pros and cons

10 things to avoid when you're trying to get pregnant

Getting pregnant: Terms you need to know

How and what to eat if you want to get pregnant