Basal Body Temperature

If you're trying to get pregnant, it's helpful to know exactly when you're ovulating so you can time sex accordingly. Many women have had success using ovulation predictor kits, which are handy because they tip you off before you ovulate. But the natural (and free) way to get a sense of your ovulation cycle is to chart your basal body temperature (BBT) and monitor your cervical mucus (CM).
What is basal body temperature?
Your basal body temperature (BBT) is your lowest body temperature in a 24-hour period. The best time to take it is when you first wake up in the morning. Before you even get out of bed to brush your teeth or start your day, pop a basal thermometer into your mouth. (This kind of thermometer shows the very tiny degree changes that a regular one can't.) It's important to try to wake up and take this reading at about the same time each morning.
Basal thermometers are available at most drugstores and usually come with a chart for recording your temperature each day so that you can start to see your body's patterns. We have a blank chart you can print out, along with step-by-step instructions on how to use it and a prefilled sample chart. You'll probably want a few copies of the blank chart because it will take at least a cycle or two to figure out your ovulation pattern.
Ovulation Calculator

Find out when you're likely to ovulate – and boost your chances of conceiving.

Before ovulation, your BBT probably ranges from 97.2 to about 97.7 degrees Fahrenheit. But two or three days after you ovulate, hormonal changes cause a rise of 0.4 to 1.0 degree in your BBT, which lasts at least until your next period. (You may notice your temperature spiking on other days here and there, but unless it stays up, you probably haven't yet ovulated.) If you become pregnant, your temperature will stay elevated throughout your pregnancy.
Of course, since a BBT chart will only tell you that you've already ovulated, the first month of recording your temperature won't necessarily be very fruitful. But by charting your BBT for a few months, you'll be able to see whether there's a pattern to your cycle, which will enable you to predict ovulation the next time around – and the best days to have sex if you want to get pregnant.
Keep in mind that if you're sick or don't take your temperature immediately after waking up, any pattern that you find may be inaccurate.
In addition to helping you predict the day of ovulation, BBT charts can also shed some light on infertility issues.