/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.
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