Measuring your basal body temperature, a.k.a. BBT, is a nifty tool that you should consider adding to your trying to conceive (TTC) arsenal. It’s an easy and cheap way to figure out when you’ve ovulated. One thing to know though is that charting your BBT will only help you figure out if you’ve ovulated after it’s already happened.

So here’s how it works — once you’ve ovulated, your BBT will shift up by at least four-tenths (0.4) of a degree Fahrenheit. (So when you’re done poking your cervix with your finger, you get to stick a thermometer in some other orifice-- ahh, the joys of TTC are endless!) If your temperature stays elevated for at least 3 days after that shift, then you know that you’ve ovulated.

Tracking BBT can tell you if you’re pregnant, too. If your BBT stays elevated for more than 15 days after ovulation, it could mean that you are preggers. (Or that you have no air conditioning and/or are wearing one of those goose down jackets indoors.)

Alternatively, if your BBT dips, then your period is most likely on its way. (Boo! When you are TTC, getting your period is even more of a bummer than just the regular instances of annoyingly getting your period.)

How to measure your BBT

Every morning when you wake up (before you even stir in bed, i.e. before you pick up your phone from your nightstand and obsessively look at social media), take your special basal thermometer and take your temperature.
You can take it orally, vaginally, or rectally — just make sure that you do it the same way each time. (For consistency. Also because taking it rectally and then after that taking it orally is a little gross, yes?) It’s also a good idea to keep your phone/Glow app within reach so you can log your BBT right away.
For the best results, set an alarm and do this at the exact same time every morning, and yes, that includes the weekends. You’re in luck because Glow can help with this, too! Simply set a daily morning reminder for yourself in the Reminders section. (If you can find a way to get your phone to play a temperature-themed song as the alarm, try a recording of “Hot, Hot, Hot” by the Merrymen, or “Hot n Cold” by Katy Perry, or “Great Balls of Fire” by Jerry Lee Lewis.)

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How much variation in BBT?