How to check your basal body temperature:
Tracking your basal body temperature (BBT) can be an effective way to monitor and predict ovulation, so you can time sex for your most fertile days and improve your chances of conception. Checking and charting your BBT is rather easy, you’ll just need a BBT thermometer and a tool to chart your temperature.
It’s important to use a thermometer specifically designed for fertility charting, such as Fairhaven Health’s Digital Basal Thermometer ($10.95). This oral-use, mercury-free thermometer has a large, easy-to-read display and is accurate to a tenth of a degree. It also has a digital memory recall function to display your most recent reading and emits a “beep” sound when peak temperature is taken.
Once you’ve taken your temperature (it only takes about two minutes), plot your temperature on a chart. You can use a free online BBT charting service like the OvaGraph website or app if you’re based in the US (learn more here). Whether you input your ovulation tracking information yourself or rely on the OvaCue to automatically upload it, using the OvaGraph app means all your fertility tracking data is stored in one place, accessible on your phone, at any time.
As you track your temperature each day, you’ll notice a shift of at least 0.4 degrees Fahrenheit after ovulation. Ideally, you’re looking for a biphasic chart: your body temperature will be lower before ovulation (during the follicular phase) than after ovulation (during the luteal phase). By inputting your temperature each day, the OvaGraph algorithms will help pinpoint your ovulation date and fertile days, based on your thermal shift. Over a few months, you can review your fertility tracking chart and look for patterns.
If your cycle is irregular, you can still chart your BBT and track your ovulation. The likelihood is that the greatest variation between your cycle lengths will occur in the follicular phase and the luteal phase should be relatively consistent (with a variation of only a day or two). Say your cycle ranges from 28 to 34 days, and your luteal phase is 14 days. Ovulation occurs somewhere between days 14 to 20, not the middle of a cycle. This is a common mistake women with long cycles make when trying to conceive.
If you’re wondering when to start charting your basal body temperature, fertility specialists advise you to start charting at the beginning of your cycle so you can better understand your body temperature and fertility. (The first day of your cycle is the first day of full menstrual bleeding.)
When is the best time to check your basal body temperature?
It’s very important to take your temperature at the same time each day, so consider setting an alarm. Try to stay within half an hour of your average time to take the most accurate reading and make sure you’ve had a minimum of five hours of sleep. It’s good practice to take your temperature before you get out of bed or even speak, so do it first thing in the morning. Leaving the thermometer at your bedside will help you remember!