What is free testosterone? A plain-language definition
Free testosterone is the portion of the hormone in your blood that is not attached to a protein. It is a small share of the total, and it is measured in some situations where the total number could mislead.
Free and total testosterone
Free and total testosterone on one order, so you get both numbers from one draw.
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Free means unbound
MedlinePlus explains that all the testosterone in your blood is either bound to proteins or unbound. The main binding proteins are sex hormone-binding globulin (SHBG) and albumin. Most testosterone is bound. The Endocrine Society guideline puts the unbound share at about 2 to 4 percent.
Bound testosterone is not as easily used by the body. MedlinePlus adds that having most of it bound is necessary for health, because it keeps the body from using too much.
Why anyone measures it
A total testosterone test counts both bound and unbound hormone. When SHBG is higher or lower than usual, the total number can give a misleading picture. Checking free testosterone helps in those cases.
The Endocrine Society guideline recommends it when total testosterone is at or near the lower limit of normal, or when a condition alters SHBG, such as obesity, diabetes, hypothyroidism, aging, or liver disease such as cirrhosis. See free vs total testosterone for the full list and the trade-offs.
How it is measured
Free testosterone can be measured directly by equilibrium dialysis, or calculated from total testosterone, SHBG and albumin. The guideline accepts calculating free testosterone by formula when equilibrium dialysis is not available.
Getting a free testosterone figure
If you want a free testosterone figure, the free and total test gives both numbers on one order. If you already have total and SHBG results, the free testosterone calculator uses a published formula to estimate free testosterone. It assumes a typical albumin level unless you enter your own, and gives an estimate, not a lab result.
- Free and total testosteroneBoth numbers on one order $99 See this test at HealthLabs
- Free testosteroneFree testosterone only $59 See this test at HealthLabs
- Total testosteroneTotal testosterone only $49 See this test at HealthLabs
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What it can’t tell you
Free testosterone is one number. It can’t diagnose a condition by itself, and the guideline says no harmonized reference range exists for it, so ranges depend on the method and the lab. See free testosterone levels.
If you have symptoms such as low sex drive or erectile dysfunction, see a clinician whatever your number is.
Free and total testosterone
$99
See this test at HealthLabsPrice checked October 2026. Not available in ND, RI, NY, NJ, MD and HI. We earn a commission on sales.
Keep reading
- Free vs total testosterone: what each measures and when it matters
Total testosterone counts bound and unbound hormone. Free counts only the unbound part. Here is what each shows and when free testosterone matters.
- Testosterone test guide: which test to get, what it shows, how to order
Which testosterone blood test to choose, what total and free results show, when to draw, how ordering works and what to do with the result.
- Testosterone lab test names on orders and results, decoded
What 'total', 'free', 'free direct', 'bioavailable' and method labels like LC-MS/MS mean on a testosterone lab order or result, and how to read the units.