A Thyroid Test You Can Do at Home: Basal Body Temperature for Thyroid Function

A woman sits cross legged on a couch, looking at her smartphone.

You’re probably familiar with basal body temperature tracking (BBT) for the Natural Family Planning method, or for tracking your hormones. But did you know that use your basal body temperature for thyroid function monitoring?

Before we even had the capacity (or knowledge) to test thyroid function through TSH, free T3, and free T4, doctors used basal metabolic rate—a metric we can test with basal body temperature—to help diagnose thyroid disease.

How Does Thyroid Function Impact BBT?

Thyroid hormone controls your body temperature through the hypothalamus. When you have thyroid dysfunction, specifically hypothyroidism, we can use BBT (which is essentially just a higher sensitivity to your temperatures with 2 numbers after the decimal) to get a really sensitive reading on your body temperature. As we work through treatment, we can use BBT to evaluate efficacy—we’d expect when your thyroid is healing and you’re creating more hormones, your temps would go up. 

Takeaway: The extremes of thyroid dysfunction (particularly hypothyroidism) can cause changes in your basal body temp.

How to Track Basal Body Temperature for Thyroid Function

  1. Because we want to record your temperature when your body’s at rest, only take your BBT in the morning, after you’ve had several hours of sleep.
  2. Take your temperature as soon as you wake up, at around the same time every day. You’ll want to take it before you even get out of bed or move around too much!
  3. Keep your smartphone or a pad and paper near your bed, so you can record each morning.
  4. Put the thermometer under your tongue and continue to rest while you wait.
  5. Record your temperature on your smartphone or paper. Some thermometers you can find online will automatically sync to an app.
  6. Repeat daily! We can find trends in your graph over time. Scenarios such as ovulation, mensuration, and other hormonal fluctuations will affect your temperatures as well, but having consistent data can help us interpret your thyroid health over time.

Over time, with thyroid healing, you should see your temperature increasing to the high 97s, and eventually, low 98s! Most people start in the low 96s, which is just crazy to me.

Takeaway: As you start to heal through root-cause treatment, you should notice a steadying of the BBT. While this isn’t the only indicator of thyroid dysfunction, it’s another tool we can use to monitor your body.