/WHAT_IT_IS
Free testosterone is the ~1–3% of total testosterone that isn't bound to SHBG or albumin — the fraction that can actually enter cells and bind to androgen receptors. For most men on TRT it's a better predictor of symptoms than total testosterone.
/NORMAL_RANGE
Lab reference is roughly 9–30 pg/mL by direct-equilibrium dialysis, the gold standard. Calculated free T (from total T + SHBG + albumin) tends to track within ~15–20% of measured values for most men.
What does high Free T mean?
- +High total testosterone with normal-to-low SHBG (TRT, AAS, or genetically low SHBG).
- +Insulin resistance or fatty liver can suppress SHBG and push free T disproportionately high.
- +Lab artifact: most automated immunoassays for free T are unreliable — use dialysis or calculate.
What does low Free T mean?
- +Low total testosterone for any reason.
- +High SHBG (aging, hyperthyroidism, liver disease, oral estrogens) — total T may be normal but free T is low.
- +Recent calorie deficit, overtraining, or chronic stress.
/ON_TRT
Free testosterone is the number to optimize on TRT. Many men with "in-range" total T still feel symptomatic because their SHBG is high enough to sequester most of it. If your free T is below the middle of the range despite a total T in the 700s, the answer usually isn't more testosterone — it's addressing the SHBG (often via dose splitting, weight loss, or addressing thyroid issues). The Vermeulen equation is the standard way to calculate free T from total T + SHBG + albumin.
/RELATED
FAQ
/01How is free testosterone calculated?+
Most clinicians use the Vermeulen equation: it takes total testosterone, SHBG, and albumin and solves for the unbound fraction using known binding affinities. It correlates well with measured (dialysis) free T and is more reliable than most automated immunoassays.
/02What's a good free T level on TRT?+
Many TRT-focused clinicians target the upper third of the reference range — roughly 20–30 pg/mL. Below 9 pg/mL is generally considered deficient regardless of total T.
/03Why is my free T low when my total T is normal?+
Almost always: high SHBG. Common causes include aging, hyperthyroidism, liver disease, low caloric intake, or oral estrogen use. Once total T is replaced, the next lever is lowering SHBG — sometimes via more frequent (smaller) injections, weight/visceral fat loss, or thyroid optimization.
/04What is free testosterone?+
Free testosterone is the small fraction of your total testosterone that isn't bound to SHBG or albumin, so it can enter cells and activate the androgen receptor. Because it's the biologically active portion, it often tracks symptoms better than total testosterone. It's typically about 1–3% of total T, most often cited near 2%.
/05What percentage of testosterone is free?+
Only about 1–3% of total testosterone circulates unbound as free testosterone, with roughly 2% being a common reference figure. Most of the rest is bound to SHBG (tightly) and albumin (loosely). Your exact percentage depends heavily on your SHBG — higher SHBG means a smaller free fraction.
/06What is the difference between calculated and measured free testosterone?+
Calculated free T is derived from total T, SHBG, and albumin using an equation like Vermeulen, while measured free T uses equilibrium dialysis, the gold-standard lab method. Calculated values usually track within about 15–20% of dialysis results and are far more reliable than the cheap automated "direct" immunoassays, which are best avoided. When possible, use either calculated free T or dialysis, not the direct analog assay.
/07What is a normal free testosterone level?+
Reference ranges vary widely by method and lab, so the number is only meaningful next to the assay used. By equilibrium dialysis the range is often roughly 9–30 pg/mL, and calculated free T ranges differ again. Because of this variability, focus on where you fall within your own lab's range and how you feel rather than comparing absolute numbers across labs.
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