How to Chart Your Basal Body Temperature and Detect Ovulation

Detecting Ovulation on a Basal Body Temperature Chart

Woman checking her fertility chart on her computer
There are a number of fertility charting websites, software programs, and even apps, for your mobile phone. Many are free. Blend Images - JGI - Jamie Grill / Getty Images

Detecting ovulation with basal body temperature (BBT) charting is relatively easy and inexpensive. Your gynecologist or reproductive endocrinologist may recommend charting to help detect when ovulation is happening or to get a better idea of your menstrual cycle patterns.

By charting your basal body temperature, you may discover that you've been missing the ideal time for sex. (That would be the three to five days before ovulation.) Or, you might discover that you're not ovulating regularly.

Over time, you may notice that you tend to ovulate on certain days in your cycle, helping you plan sexual intercourse that has the best chance of resulting in pregnancy.

Choosing a Basal Body Temperature Chart

The first step to charting your basal body temperature is getting a chart to record your temperature.

You can find sample charts in some fertility books, such as Take Charge of Your Fertility (Harper Perennial, 1995)—a book considered by many to be the go-to resource for basal body temperature charting guidance.

Another option for charting is fertility awareness software, also known as fertility calendars. There are several fertility calendar options online, and several fertility apps for your phone. Many of them are free.

You could also make your own graph. If you make your own, you'll want to plot the temperature along the vertical, allowing one-tenth of a degree for each square. Along the horizontal, you'll have the days of your cycle.

Most women prefer using the computer because you can log a ton of information and reduce the chance of human error. Most ovulation software will automatically indicate when ovulation likely occurred. If you try plotting the temperature yourself, you might worry about making a mistake.

Once you have something to record your temperature on, it's time to start taking your basal body temperature.

How to Take and Chart Your Basal Body Temperature

woman taking her temperature in bed for fertility charting
Keep your thermometer next to your bed. You shouldn't sit up or walk around before taking your body basal temperature. Larry Dale Gordon / Getty Images

Now that you have a BBT chart picked out, you'll now need to get a thermometer.

There are tons of specially made basal body thermometers for sale.

While some come with interesting features, the honest truth is that any good, regular thermometer will work.

Taking your Basal Body Temperature

Taking your basal body temperature isn't too hard. There are a few must-keep rules:

  • You need to take it at the same time (plus or minus no more than 30 minutes) every morning. For example, if you take it at 7:30 am, you don't want to take it earlier than 7 am or later than 8 am on other days.
  • You can not get up, sit up, walk around, or go to the bathroom before taking your temperature. The minute after you wake up, you need to pop the thermometer in your mouth. (Which you hopefully placed within hand's reach the night before!)
  • You need to have had at least three to four straight hours of sleep before taking your temperature in the morning. If you stayed up all night, or you woke up and walked around at night repeatedly, it will throw off your results.
  • You should use the same thermometer throughout the cycle. (If you buy a new one, start using it on day one of the next cycle.)

If you want more details on taking your BBT temperature, read this article on how to take your basal body temperature.

When to Start Charting Your Cycle

Ideally, you should start charting on the first day of your period and continue to take your BBT temperature every morning throughout the entire cycle.

Every day, mark your waking basal body temperature, along with the time that you took your temperature.

After you have experience with charting, you may discover that you can skip the first few days of your period and start taking your temperature around day 5 or 7. Until you know when you tend to ovulate, though, it's best to take your temperature all the way through the cycle.

Identifying Ovulation on the Basal Body Temperature Chart

Basal Body Temperature Chart with Ovulation / iStockPhoto
Basal Body Temperature Chart with Ovulation. Photo © iStockPhoto

With basal body temperature charting, you're looking for an overall pattern, as opposed to a temperature spike here or there.

Your temperature may rise and fall as your cycle progresses, but you should notice a biphasic pattern after ovulation. This means that before ovulation, the temperatures are on average lower than they are after ovulation.

For example, in the photo above, ovulation occurred on the day the temperature dipped. We know this because the temperatures after this day are relatively higher than they were earlier in the cycle.

After you see at least three higher-than-average temperatures in a row, you can most likely say that ovulation occurred on the day before the first high temperature.

If you've been tracking your cervical mucus, then you can be even more sure ovulation occurred on the day before if you noticed fertile cervical mucus on the days leading up to the temperature rise.

BBT Chart Dips

Basal body temperature chart with ovulation and implantation dip
Ovulation occurred on Day 15, and the implantation dip is on Day 23 (which is eight days past ovulation.). Rachel Gurevich

The primary pattern you are looking for on a basal body temperature chart is the upward shift in temperature that occurs just after ovulation. That said, there are other temperature changes that can indicate signs of ovulation or (maybe) even pregnancy.   

If you're lucky, you may notice a strong dip in temperature on the day of ovulation. Not every woman gets this nice heads up. If you do notice a consistent dip in temperature before the rise from month to month, you should be sure to have sexual intercourse on that day.

Some women attempt to detect early pregnancy using their BBT charts by looking for implantation dips or triphasic chart patterns. An implantation dip is when your temperature drops about 7 to 10 days after ovulation and then goes right back up. (See photo above for an example.) A triphasic pattern is when there is a third sustained rise in temperature about a week after the ovulation-triggered rise.

Unfortunately, having an implantation dip or triphasic pattern can't tell you with any certainty if you're pregnant, but research has found that these patterns are slightly more likely to show up if you conceived.

How to Use Your Basal Body Temperature Chart to Help You Get Pregnant

Woman showing her fertility chart to her doctor
Bring your fertility charts to your doctor appointment. Your doctor can use the information to help diagnose ovulation problems. Hero Images / Getty Images

Getting pregnant is the entire reason that you've started using a basal body temperature chart. So, how can you use this information to help you get pregnant?

Look for Patterns

Do you tend to ovulate on certain days of your cycle? Use this information to time intercourse better.

For example, if over a three-month period you note that ovulation occurred on days 11, 12 and 15, then on your next cycle, you probably want to time sex between days 6 through 16, with special attention toward days 11 through 15.

Remember, also, that you don't need to have sex on the day of ovulation to get pregnant.

If you have sex just a few times during those days before ovulation, that should be enough to get the sperm to the egg in time. Some couples try to have sex every other day the week before they expect ovulation. This is also a good plan.

Other Signs and Details to Note on a Basal Body Temperature Chart

Nurse or doctor sleeping on a gurney in a hospital
Shift work can throw off your body basal temperatures. If you work the night shift, charting your BBT is probably not for you. Andersen Ross / Getty Images

Basal body temperature charting is a great way to see if and when you are ovulating, but it's not so great at predicting ovulation.

Your temperature will only rise and remain elevated after ovulation. By then, the ideal time for baby-making sex will have passed.

For this reason, you should also track your cervical mucus changes on your chart.

Here are some other things you may want to record on a BBT chart:

  • Days you have sex: This will help you and your doctor see if you're timing intercourse right. There are only five to seven days within each cycle when it's possible for sex to lead to pregnancy. The two to three days right before ovulation are best. You don't want to miss your window of opportunity.

    Another reason for charting when you have sex is to show how often you're having sexual intercourse. If male factor infertility is an issue, having sex every day may decrease your chances for pregnancy. On the other hand, having sex just once within the approaching days to ovulation may not be enough. Read more about how often to have sex.
  • Cervical position: Besides tracking your cervical mucus, you can also track your cervical position to help predict ovulation. Your cervix will become higher, softer, and more open as ovulation approaches. After ovulation, the cervix becomes more firm, lower, and closed (or partially closed).
  • Illness, stress, or difficulty sleeping: Even a relatively benign cold can mess with your BBT charting. If sinus congestion forces you to sleep with your mouth open, for example, your temperature may be thrown off. Also, poor sleeping habits can skew the results.
  • Ovulation predictor kit results: If you're also using an ovulation predictor kit, or any other form of ovulation prediction such as a saliva ferning kit, you should mark down these results on your chart.

Share Your Charts With Your Doctor

One huge benefit to basal body temperature charting is it can help spot potential problems.

For example, if you notice that you don't get a shift in temperature, you may not be ovulating. Also, if the time between ovulation and the first day of your menstrual cycle is ten days or less, your luteal phase may be too short to get pregnant.

If you notice problems like this, you do not need to wait months before seeing your doctor. You can bring your charts to your doctor and voice your concerns right away.


Fertility Awareness: Natural Family Planning. American Pregnancy Association.

Patient Fact Sheet: Ovulation Detection. American Society of Reproductive Medicine.