How to Calculate Your T3 Reverse T3 Ratio

Young female doctor examining senior woman’s throat isolated over white background

Triiodothyronine (T3) is your most active thyroid hormone that ‘revs’ up metabolism to keep your body humming. 

So what happens when T3 is low? Or even worse, T3 is low and the body is also producing an abnormal amount of reverse T3 which is an inactive form of T3?

Let’s Cover Some Basics Before We Discuss Your T3 Reverse T3 Ratio

When your body is working well it converts thyroxine (T4) to both T3 and ‘reverse T3’.

It’s important to note reverse T3 (RT3) is an inactive form of T3.

The body produces an ideal ratio of T3 to reverse T3 to control metabolism. Only small amounts of reverse T3 are normally produced as this hormone slows metabolism. As a consequence, reverse T3 is swiftly eliminated when it’s not required to slow metabolic activity.

However, the T3 to reverse T3 (RT3) ratio can get out of balance.

Excessive reverse T3 leads to a low thyroid disorder called ‘reverse T3 dominance’. And as you can imagine, this thyroid disorder triggers many of the symptoms commonly associated with hypothyroidism.

Routine Testing Should Include RT3

Getting reverse T3 (RT3) tested is controversial. For the most part it’s not generally recommended for routine evaluation of thyroid disorders. But functional medicine doctors and Naturopaths consider the RT3 test essential as part of routine testing. The reason is, excess RT3 sabotages proper thyroid function.

If you are having a hard time getting this test there is good news. Companies such as i-screen, Australia and True Health Labs, USA offer a range of thyroid lab tests, including the RT3 test. You can order and pay for the tests you want online. No referral necessary.

How To Calculate Your T3 Reverse T3 Ratio

Before you get started with calculating your T3 to reverse T3 ratio you need your free T3 and reverse T3 test results. Once you have these, divide free T3 by the total reverse T3 and multiply this by 100. What is your result?

The reference range currently used by functional pathology labs is 1.200 – 2.200.

When the T3/reverse T3 ratio is at the lower end, or below this range it suggests there’s a problem with excess RT3.

Your thyroid blood results can be a little confusing. Here is an example to help explain how you can calculate your own T3/reverse T3 ratio using pmol/L test results.

EXAMPLE: The free T3 test result is 4.3 pmol/L and reverse T3 is 704 pmol/L. To work out the free T3 reverse T3 ratio:

Take 4.3 and divide by 704 then multiply this result by 100. The ratio is 0.610 which is well below the healthy range.

Is A Single T3 Thyroid Medication The Best Solution?

A single T4-only medication is not recommended when your reverse T3 is high.

The T4-only medication provides the body with more T4 that has the potential to be converted through to reverse T3. It can perpetuate an excess reverse T3 problem.

Switching to a T3 only medication may be the solution. This will supply the body with the T3 it needs, and over time it will help clear excess reverse T3 from the thyroid receptors.

It’s generally accepted a single T3 thyroid medication may take a little while to work as the pool of reverse T3 needs time to clear from the body.

After some time you may find changing from a T3-only medication to a combination of T4/T3 is more effective in managing this thyroid disorder. It really depends on what your body needs. As you can imagine, it’s vital to work with a thyroid-literate doctor to navigate the best holistic treatment strategy.

Please note: This post contains affiliate links, to find out more about my affiliate policy please refer to my Terms of Service.


  • Here’s What You Need To Know About Reverse T3 DominanceIf you’ve been told your thyroid test results are ‘normal’ you may want to learn more about reverse T3 dominance which can trigger a long list of hypothyroid symptoms. Here’s what you need to know about reverse T3 dominance, and…
  • The Symptoms of High Reverse T3 You Need To Know AboutWorried about symptoms of high reverse T3? Reverse T3 (RT3) is considered a biologically inactive thyroid hormone. For this reason high levels of this hormone are associated with a range of hypothyroid symptoms. The Symptoms of High Reverse T3 You…
  • The Top Five Reasons Why Your Body Creates Excess Reverse T3Reverse T3 is the ‘hibernation hormone’ as too much of this thyroid hormone triggers hypothyroid symptoms. These symptoms can include ongoing fatigue, depressed mood, hair loss, muscle weakness, low blood pressure, a slower than normal pulse rate, and other signs…
  • Top 5 Thyroid Tests: The Best Tests To Discuss With Your DoctorWhile routine testing of thyroid stimulating hormone (TSH) plays an important role in thyroid assessment it doesn’t provide the full picture. Here are the top 5 thyroid tests that will help you discover what’s really going on with your thyroid…

Recent Posts