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Hormone health

Free Testosterone

Also known as: Free T, Bioactive testosterone, Calculated free testosterone (cFT), Non-sex hormone-binding globulin (non-SHBG), Bound testosterone, Bioavailable testosterone

Free testosterone is the small portion of circulating testosterone that isn’t bound to proteins like sex hormone binding globulin (SHBG) and albumin. Because it’s unbound, this fraction can move into tissues and activate androgen receptors, influencing everything from energy and mood to sexual function and muscle mass. 

A free testosterone test measures that bioactive fraction. Providers use the test in men to help evaluate possible testosterone deficiency, particularly when the total testosterone level alone may not tell the whole story. 

There are two main ways to measure free testosterone. The first is “calculated free testosterone,” which is estimated using total testosterone, SHBG, and albumin levels. The second is “equilibrium dialysis,” a more complex lab method that directly measures free testosterone — this method is typically more accurate than the calculated method.

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Key takeaways

  • Sample required: Blood

  • Tests for: The unbound (free) fraction of testosterone that can enter cells and exert biologic effects. Test results help evaluate suspected testosterone deficiency

  • Healthy/normal range: 20–190 picograms per milliliter (pg/mL) in adult males (calculated) or 5–21 nanograms per deciliter (ng/dL) (equilibrium dialysis)

What can a free testosterone test tell you?

Clinically, testing free testosterone can add value when:

  • Diagnosing hypogonadism (testosterone deficiency). If total testosterone is low or borderline low – below 300 nanograms per deciliter (ng/dL) – your provider may test your free testosterone levels and assess symptoms before confirming a diagnosis.

  • Diagnosing hypogonadism despite normal testosterone levels. If your total testosterone is normal, but you have symptoms of hypogonadism, providers may test free testosterone. Research supports that free testosterone has a strong association with hypogonadal signs and symptoms. 

  • Suspecting a problem with sex hormone–binding globulin (SHBG). Measuring free testosterone can be helpful for investigating low testosterone when SHBG levels are abnormal. Such an abnormality may occur with aging, obesity, hypothyroidism, type 2 diabetes, or liver disease.

The Endocrine Society advises against routine screening of men in the general population for hypogonadism. According to its guidelines, providers can only diagnose low testosterone in men with regular symptoms and “unequivocally and consistently low” serum testosterone. Testing total testosterone happens first. A provider may consider a free testosterone test when total testosterone is borderline or SHBG is abnormal.

What is being tested? 

In men, the Leydig cells in the testes and, to a lesser extent, the adrenal glands are responsible for producing testosterone. Most testosterone travels through the bloodstream attached to proteins — primarily sex hormone–binding globulin and, to a lesser degree, albumin. Only about 2–3 percent of total testosterone circulates freely. This free testosterone is what’s available to enter cells and activate androgen receptors, driving effects on muscle mass, bone density, mood, and sexual function.

Balanced free testosterone levels help maintain energy, fertility, and overall well-being. If your levels are low, you may experience symptoms like decreased libido, fatigue, reduced muscle mass, and mood changes. Because free testosterone represents the biologically active portion of the hormone, measuring it can provide a clearer picture of how the androgen system is functioning — especially when total testosterone results don’t align with symptoms.

Where is the free testosterone test typically included?

Free testosterone is not part of standard metabolic panels like the basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). It is usually included in:

  • Standard hormone panels. With total testosterone, SHBG, and albumin.

  • Comprehensive hormone panel. With total testosterone, SHBG, albumin, estradiol, and prolactin.

  • Male fertility investigations. With total testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, and a semen sample.

Who should get a free testosterone test?

A provider may order free testosterone testing if you have symptoms of testosterone deficiency, including:

  • Low libido

  • Erectile dysfunction (ED)

  • Decreased morning erections

  • Fatigue

  • Reduced muscle ass

  • Low bone density

  • Less body hair

  • Increased body fat

  • Brain fog

  • Mood changes

  • Gynecomastia (increased breast tissue in men)

Providers may also suggest testing free testosterone if you have a borderline total testosterone result or if they suspect SHBG abnormalities.

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Not available in all 50 states. Eligibility and provider order required. Lab results alone are not intended to diagnose, treat, or cure any condition. A provider will reach out about critical results and plans include access to 24/7 provider messaging.

Images for illustrative purposes only.

Frequently asked questions

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What causes changes in free testosterone levels?

Free testosterone levels can vary due to lifestyle factors, medication use, and normal biological fluctuations. 

High free testosterone may occur when sex hormone–binding globulin (SHBG) levels are low, which can happen with conditions like obesity, diabetes, or hypothyroidism. It may also result from rare causes such as androgen-secreting tumors or Cushing’s syndrome. Increases in free testosterone can also stem from testosterone-based therapies — like testosterone replacement therapy, enclomiphene, or human chorionic gonadotropin (hCG) — as well as from anabolic steroid use or even exercise.

Low free testosterone can be linked to primary hypogonadism (testicular failure) or secondary hypogonadism (impaired communication between the brain and the testes). Levels also tend to decline with age or when SHBG levels are elevated due to conditions such as liver disease, hyperthyroidism, or anorexia. Certain medications (like anticonvulsants), lifestyle habits (including smoking, alcohol, caffeine, stress, or lack of sleep), and calorie restriction can further reduce free testosterone levels.

What’s the typical reference range for free testosterone?

The typical reference range for adult males is 20–190 pg/mL using the calculated method and 5–21 ng/dL using equilibrium dialysis (ranges are lab-specific).

Can you do a free testosterone test at home? 

Yes, some at-home testosterone testing kits estimate calculated free testosterone using total testosterone, SHBG, and albumin from a dried blood or venous sample. However, the reference method (equilibrium dialysis) and many confirmatory tests are performed in clinical laboratories. Discuss the pros and cons of at-home testing with your provider. 

Is fasting required for a free testosterone test?

Guidelines recommend testing in the morning, and fasting can both improve consistency and reduce variability for total testosterone. Always follow your lab and provider instructions.

How long do results take?

Turnaround times for results vary by lab and method. Equilibrium dialysis often takes longer than a calculated result because it’s more complex. Ask your laboratory or provider for specifics. 

How often should I get tested?

There’s no routine interval for testing free testosterone. In men being evaluated for low T symptoms, clinicians start with two morning total testosterone tests. Free testosterone is added when appropriate. If treatment begins, monitoring typically includes follow-up testing.

Does insurance typically cover free testosterone testing?

Coverage depends on your plan and condition. Many insurers cover testosterone testing when medically necessary for evaluating symptoms, but you should confirm with your carrier. Hims doesn’t require insurance coverage for testing.

What tests are related to this biomarker?

• Total testosterone

• SHBG 

• Albumin 

• Luteinizing hormone

• Follicle-stimulating hormone

• Prolactin

• Estradiol 

• Thyroid function

The information provided here is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk to a qualified healthcare provider about your specific health concerns.

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Estradiol

Estradiol is a form of estrogen that men make from testosterone. At a healthy level, it supports bone strength, libido, brain function, and heart health.

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Follicle Stimulating Hormone (FSH)

Follicle-stimulating hormone (FSH) is a hormone produced by a part of your brain called the pituitary. It is essential for sperm production and reproductive function. 

Learn more about Follicle Stimulating Hormone (FSH)

Luteinizing Hormone (LH)

Luteinizing hormone (LH) is produced by a part of your brain called the pituitary. It is a crucial hormone that stimulates testosterone production in the testicles. 

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Sex Hormone Binding Globulin (SHBG)

Sex hormone-binding globulin (SHBG) is a protein that carries testosterone and estrogen in the bloodstream. Unlike some other carrier proteins, it holds on to testosterone and estrogen very tightly, making them less available for your body to use.

Learn more about Sex Hormone Binding Globulin (SHBG)

Total Testosterone

Total testosterone is a measurement of all of the testosterone in your bloodstream. It counts all forms of the hormone in your blood, including free molecules and those attached to proteins like albumin and SHBG. This measurement is the go-to to determine if someone has a testosterone deficiency.

Learn more about Total Testosterone

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Reviewed by Darragh O'Carroll, MD

Published 11/19/2025