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What is Free Testosterone

Free Testosterone Definition: What You Need to Know

Testosterone is the primary male sex hormone that is involved in many different functions in the body. This hormone is especially important for men as it plays a vital role in supporting libido, muscle mass and energy levels. But while most of this hormone is bound, there’s also an unbound, free version. So, what is free testosterone?

Free testosterone is the unbound, bioavailable type of testosterone found in the body.

This form of testosterone is not bound to any molecules, indicating that it’s readily available to be used by the body for various processes and functions.

This means that free T can easily enter cells and activate the receptors to deliver powerful benefits such as increased sex drive, improved muscle mass and lowered body fat.

However, note that free testosterone constitutes only around 2% of total testosterone that floats in the bloodstream (1).

But despite making up only a minuscule amount of total T, free testosterone is still considered to be a critical factor for determining androgen deficiency issues in men.

In fact, a 2014 study published in the Advances in Clinical Chemistry journal reveals that free T is an important measurement for diagnosing impaired testosterone production in men – hypogonadism (2).


What Does Free Testosterone Do?

Free testosterone is responsible for binding to testosterone receptors within the body’s cells, which enables free testosterone’s functionality, namely cell replication in the muscles and bones.

Additionally, free T plays a major role in the formation of secondary sexual characteristics in men, such as:

Since free testosterone is considered as the metabolically active fraction of testosterone, free T can be used as a diagnostic tool for certain male disorders.

More specifically, disorders like androgen deficiency in men – male hypogonadism, which stands for impaired testosterone production in the body.

Free testosterone levels can also be used to provide further information to your doctor if your total T turns out to be low, following a testosterone levels test.


What is Free Testosterone, confused man holding a dumbbell in his left hand

What is the Difference Between Total Testosterone and Free Testosterone?

Total testosterone refers to the overall amount of testosterone in the bloodstream, while free testosterone stands for only the unbound (i.e. free) bioavailable type of testosterone.

Only about 2% of all testosterone in the body is free, while the rest 98% are bound.

It’s important to note that although free testosterone is part of the total testosterone in the body, its share of the overall amount is minuscule.

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Total testosterone equals to 100% of all testosterone in the bloodstream, while free T makes up only 2% of this amount.

And when someone mentions testosterone levels, they’re most likely referring to the grand total of this hormone, not a specific type.

In fact, there are 3 specific kinds of testosterone found in the human body that are summarized in 2 main categories:

Bioavailable vs Bound Testosterone

  • Bioavailable testosterone: Free testosterone and albumin-bound testosterone
  • Bound testosterone: Sex hormone-binding globulin-bound (SHBG) testosterone

Now, the SHBG-bound is self-explanatory as it’s the only form of the hormone that’s considered ‘bound’.

But albumin-bound T is actually considered bioavailable testosterone because the albumin protein has a lower affinity to testosterone.

Albumin-bound testosterone can still be used as a reserve supply by tissues, particularly when free T levels become low.


What is Free Testosterone, a muscular man standing inside a gym

What are the Benefits of Free Testosterone?

The benefits of free testosterone are the same as the benefits associated with testosterone in general, such as:

  • Increased sex drive and libido
  • Improved muscle and bone mass
  • Elevated mood and energy levels
  • Decreased body fat

However, the testosterone-related benefits even stretch as far as mental health and mood.

A 2015 scientific review published in the Frontiers in Neuroscience concludes that testosterone can reduce anxiety and even act as an anti-depressant (3).

Moreover, studies show that testosterone plays a key role in regulating the secondary sex characteristics in men, namely anabolic effects, voice deepening and hair patterns (4).

But this hormone is also incredibly important for the mental health of men.

Research from 2020 reveals that testosterone is vital for supporting behavior, mood and the quality of life in men across all ages (5).

Even more intriguing is the fact that the same study also links low T levels with symptoms of depression.

All of this means that there are myriad benefits associated with free T (and testosterone in general), some even related to mental health and mood.


What is Free Testosterone, a man doing bench press with a spotter

How Do You Raise Free Testosterone?

You raise your free testosterone levels the same way you would increase your total T levels, or more specifically by means of:

  • Exercise with weights i.e. weightlifting (6)
  • Lower stress and cortisol levels (7)
  • Get enough quality and restful sleep (8)
  • Avoid excessive alcohol consumption (9)
  • Get direct exposure to sunlight or use a vitamin D supplement (10)

All of the methods mentioned above can be summarized by this – living a healthy lifestyle is vital for your overall well-being, not only for your hormones.

So do your best to minimize any risk factors such as drinking and smoking, without neglecting proven testosterone-boosting methods such as resistance training.


What is free testosterone, Free Testosterone Levels by Age Chart with reference ranges

Free Testosterone Levels by Age Chart

Based on the reference ranges provided by the Methodist Pathology Center in Omaha, Nebraska, the free testosterone levels by age chart for men look like this:

  • 14 to 15 years – 3 to 138 pg/mL
  • 15 to 16 years – 38 to 173 pg/mL
  • 18+ years (adults) – 47 to 244 pg/mL

However, your test might only reveal your total T levels.

How do you figure out how much free T’s coursing through your veins then?

A rough estimate would be to divide your total testosterone by 2% as that’s approximately how much free testosterone the average male has.

The percentage of free testosterone in adult males is around 1.6% to 2.9%.

But the most accurate reading will always be a specific blood test that includes free testosterone levels.

This way you will be able to see if you have normal testosterone levels as a whole and if your free T falls between the 1.6-2.9% of total T range.


What is Free Testosterone, depressed man sitting on a table

What Causes Low Free Testosterone?

Low free testosterone is mainly caused by androgen deficiency – a state in which the body doesn’t have enough male sex hormones (e.g. testosterone) that are needed to maintain adequate health, according to a 2016 study published in The Journal of Clinical Endocrinology & Metabolism (11).

The same research also mentions that low T levels are a sign of androgen deficiency, even if total T appears normal.

Experts from the same study courtesy of The Journal of Clinical Endocrinology & Metabolism suggest that men with suspected low testosterone symptoms should get their free testosterone checked as an assessment tool.

This is recommended due to the fact that most tests only target total testosterone levels.

And even your total T falls within normal ranges, you could still be experiencing male hypogonadism symptoms, such as:

  • Decreased energy
  • Reduced muscle and bone mass
  • Erectile dysfunction
  • Depression
  • Infertility
  • Gynecomastia (man boobs)

Although normal T and low free T are associated with androgen deficiency symptoms, middle-aged and elderly men seem to be particularly affected, according to the 2016 research mentioned earlier.

As a result, free T levels can be used as an early assessment of androgen deficiency, particularly in middle-aged or elderly and also obese men.


What is Free Testosterone, man working out at an outdoors gym

How Do You Treat Low Free Testosterone?

There are two methods for treating low free testosterone:

  • Natural (lifestyle changes, supplements, vitamins etc.)
  • Artificial (testosterone replacement therapy i.e. testosterone medication)

Please keep in mind that you can combine and use both methods simultaneously or you can decide to go with only one of the two techniques for dealing with low T.

In fact, you have to treat low free T the same way you’d treat low T in general.

1. The Natural Way

  • Become physically active – Men who are physically active have a superior anabolic hormonal environment (more testosterone), as well as healthier semen production than sedentary folks (12)
  • Reduce your stress – Stress and stressful situations lead to erratic variations in T levels in men (13)
  • Get plenty of restful sleep – Not getting enough sleep leads to a reduction in T levels, with relevant studies showing that 1 week of restricted sleep results in a drop of 15% (14)
  • Supplements – Vitamins and testosterone boosters can help, especially those containing vitamin Das it has been proven to increase free testosterone levels in men (15)
  • Lose body fat – Obesity in men is directly related to lower T levels, as guys between 14-20 are reported to have roughly 50% less testosterone on average than their non-obese counterparts (16)

2. The Artificial Way

Testosterone replacement therapy (TRT) is an artificial method used for treating men who suffer from abnormally low levels of T.

This testosterone medicine is prescribed by a doctor who needs to first assess your low testosterone symptoms and signs decide if TRT is right for you.

And if your doctor thinks that natural solutions won’t be effective enough in your case, they can prescribe you one of the following types of TRT:

  • Injections – A particular type of synthetic testosterone is injected every 7-14 days
  • Skin patch – A small patch is applied to the skin every day (in the evening)
  • Pellets – A pellet is implanted under the skin (typically somewhere around the buttocks or hips) that is then replaced every 3-6 months
  • Gel – A topical gel is applied every day to the skin over the thighs, upper arms or shoulders
  • Oral therapy – Either a capsule is consumed or a tablet is attached to the inner cheek or gum 2 times a day

However, it’s not all roses and rainbows as TRT carries certain health risks that are worth mentioning.

A 2014 study published in the Indian Journal of Urology shows that testosterone replacement therapy has been linked to potential risks such as (17):

  • Cardiovascular disease
  • Prostate cancer
  • Gynecomastia/breast cancer
  • Acne
  • Infertility

This is why it’s crucial to always talk to your doctor and evaluate all the potential benefits and risks of TRT.


What is Free Testosterone, sports team stacking their hands together

Is Free Testosterone Important?

Yes, free testosterone and testosterone, in general, is undoubtedly the most important hormone for men as it is responsible developing and supporting vital functions such as:

  • Growth
  •  Secondary sexual characteristics
  • Libido
  • Spermatogenesis (the production of sperm in the testes)

Free testosterone is also important for diagnosing specific disorders such as androgen deficiency in men (a.k.a. male hypogonadism), according to a 2014 study by the Advances in Clinical Chemistry (18).

Last but not least, free testosterone is an integral part of maintaining a healthy hormonal balance in men.



Overall, free testosterone stands for testosterone that is not bound to any molecules, hence being ‘free’ and ‘unbound’.

Although it makes up only about 2% of total testosterone, free T still plays a part in supporting healthy total T levels in men.

Thus, it’s not surprising that researchers suggest using free T levels to assess signs of hypogonadism, even when the overall amount of T in the body is in the normal range.

And while you would increase your free testosterone the same way you’d boost your total testosterone, keeping an eye on your free T levels can be a good idea as a preventative measure.

Now, have you ever checked your free testosterone levels by doing a specific blood test?

Also, have you ever felt chronic fatigue, low libido, lack of motivation, weight gain or loss of muscle mass even if your total T levels appear normal?

Let us know by dropping a comment below!



What is free testosterone and how is it different from total testosterone?

Free testosterone is the portion of testosterone in the blood that is not bound to proteins, while total testosterone includes both bound and unbound forms.

Free testosterone is the biologically active form of the hormone and can interact with androgen receptors in tissues throughout the body.

Why is measuring free testosterone important?

Measuring free testosterone levels can provide important information about a person’s hormonal balance and can help diagnose certain medical conditions such as hypogonadism (low testosterone levels), polycystic ovary syndrome (PCOS), and hirsutism (excessive hair growth).

It can also help monitor the effectiveness of testosterone replacement therapy in men with low testosterone levels.

What are normal free testosterone levels?

Normal free testosterone levels can vary depending on a person’s age, sex, and overall health.

Generally, normal ranges for men are between 50-210 pg/mL, while for women, normal ranges are between 0.1-6.4 pg/mL.

However, it’s important to note that the specific normal range can vary depending on the laboratory performing the test.

What factors can affect free testosterone levels?

Several factors can affect free testosterone levels, including age, sex, obesity, chronic illness, certain medications (such as opioids), and hormonal imbalances.

Lifestyle factors, such as diet and exercise, can also play a role in testosterone levels. For example, research suggests that exercise can increase free testosterone levels in both men and women.

How is free testosterone measured?

Free testosterone is typically measured using a blood test.

There are two main methods for measuring free testosterone: direct and indirect.

The direct method involves separating free testosterone from other forms of the hormone using a technique called equilibrium dialysis.

The indirect method involves calculating free testosterone levels based on the amount of testosterone and sex hormone-binding globulin (SHBG) in the blood.

Each method has its advantages and disadvantages, and the specific method used can depend on factors such as cost and availability.

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I've been fascinated by natural male hormone optimization since 2016. And ever since I've been going through boatloads of different meta-analyses and scientific data associated with increasing testosterone levels naturally. I hold a PhD degree in public health and have 10+ scientific publications on Google Scholar. Thus, in my collective work here you'll find helpful tricks, natural remedies, detailed product reviews (including stuff I've personally tried)... and more!

4 thoughts on “Free Testosterone Definition: What You Need to Know”

  1. Informative article, thanks. I have lots of questions, and I wonder if you can clarify.
    I am 69 yrs old, 25 pounds overweight, all in the belly, type II diabetes for 25 years (controlled, last A1c was 6.5), cannot seem to lose weight, even with low cal, semi keto diet. I work out 6 days a week, with cardio and crunches all 6 days, and weight lifting 2 days per week for upper body, 2 days a week for legs.
    I have lots of symptoms of low T (overweight, body hair loss, can’t build muscle mass even though working out 6 days a week, ED, brain fog/lack of focus, memory issues, fatigue, low motivation), so my internist had me tested for low T with the following results:
    Testosterone total is 446 ng/dL (low normal), Albumin 4.3 g/dL (normal), SHBG 52 nmol/L (normal), but Free T 40.2 pg/mL (low) and Bioavailable T 79.2 ng/dL (low).
    My Endocrinologist says she only looks at Total T, and she does not want me to do TRT, because of potential red blood cell increase and potential heart/stroke and prostate issues. Is this the old way of thinking? What are the odds of developing problems such as these, or would it be safe to try TRT for a few months to see if these symptoms resolve? What about long term?
    (My endo is a slim, attractive 40 yr old female, not sure if she even understands how it feels to deal with this. Her main focus is my diabetes, which I appreciate, but quality of life should count, unless it is too dangerous to pursue something like TRT).
    I would like feel better, and though I am not a kid, it seems pretty grim to live with all these issues for the next 10 to 20 years. I also hear that diabetes and low T go hand in hand, with no indication of which is the chicken and which is the egg. Wouldn’t it be nice if TRT could help with insulin sensitivity as well!
    If TRT could help to drive my diabetes down and help me lose weight and feel better, that would be great. But the more I read, the more confused I get. Any suggestions, advise or other material you can provide to help me understand these numbers and how they impact my situation and what I can do about it would be wonderful.
    Thanks very much.

    1. Hey there David and welcome to Tnerd!

      Sorry to hear about your diabetes-related problems and not seeing results from hitting the gym on a regular basis.

      First of all – I’d look into overtraining. Working out 6 times a week is way too much for most people, especially regular guys who simply want to build some muscle. Better focus on an x3/week full-body routine with medium volume and drink more water if you aren’t already.

      TRT is basically injecting synthetic testosterone into your body i.e. the same thing as what steroid users do. Personally, I’m against the use of synthetic T injections, patches or whatever if your total T isn’t too low, but yours seems within the normal range.

      I see that you’re already doing some things right (you work out regularly), so here are a few extra suggestions that can help to boost your low free T:

      – Get more quality, restful sleep
      – Reduce your stress
      – Eat healthy fats (e.g. avocado, olive oil, fish oil)
      – Skip any junk food
      – Avoid alcohol (including beer)
      – Try a natural testosterone boosting supplement (have a look at my Testogen Review: Boost Your Testosterone Levels by 203%!?)

      I totally understand your point regarding maintaining a certain quality of life.

      Thus, if your doctor doesn’t recommend TRT at this stage, ask her about dietary supplements and the other lifestyle-related recommendations mentioned above.

      Let me know how things go.

      Cheers and God bless,

      — Simon

  2. Hey there Simon!

    Very informative article, appreciate the insight. Here’s my situation, maybe you have an idea how to proceed? I am a male just about to turn 50, was diagnosed with secondary hypogonadism 4 years ago and have been on trt since that time. My first endocrinologist was a joke and had me taking trt injections at 3 week intervals which was doing me no good other than a sore backside when I got the shot. I was able to find a great doctor in my area which helped me tremendously to get my testosterone optimized, currently sitting at 32.4 nmol/L which is where he likes me. I was told he took me as far as he could and sent me back to my family doctor which is troubling as they just don’t understand what’s happening. In the past 12 months or so I have noticed a severe decline in my overall wellness and am experiencing the same symptoms I was 4 years ago, brain fog, low motivation (zero actually), poor sex drive, low endurance and weight gain. my recent blood work show’s a free T level of 1169 pmol/L which is high. I have a meeting with my doctor coming up to see about solving the mystery of why I feel so lousy. I am concerned for adrenal fatigue among other issues. other than my testosterone issues I am a generally healthy guy. Any suggestions which direction to go?

    Appreciate any feedback you may have.



    1. Hello Clayton and welcome to Tnerd!

      Sorry to hear about your symptoms.

      An experienced endocrinologist should be able to figure it out, so I’d suggest finding one in your area.

      Your T levels are high enough already, but too much testosterone might be metabolized to estrogen. As your T levels go up, so do your estrogen levels. But this is something that your endocrinologist should already know, and I’m assuming your TRT dosage is about right.

      Have you done a complete blood count anytime soon?

      Personally, I’ll look for a second opinion, while also excluding other potential culprits like chronic fatigue syndrome.

      Cheers and God bless,

      — Simon

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Although I'm a Ph.D., I'm not a medical doctor. The content on this websites is meant for educational and informational purposes only, it's not medical advice. The information and other content found on this website is not a substitute for professional medical expertise or treatment.