Free Testosterone Calculator
Estimate your free and bioavailable testosterone from a standard lab panel — total testosterone, SHBG, and albumin — using the clinical Vermeulen equation.
Enter your total testosterone and SHBG (from a blood test) to estimate free and bioavailable testosterone.
Calculated with the Vermeulen equation. For reference, typical adult-male free testosterone is roughly 5–21 ng/dL (50–210 pg/mL), but ranges vary by lab, assay, and age. This tool is for general education only — not a medical device, diagnosis, or treatment recommendation. Interpret results with a licensed healthcare provider.
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Why free testosterone matters more than total
Most of the testosterone in your blood is bound to proteins — tightly to SHBG and loosely to albumin — and isn't directly available to your tissues. Only the free fraction (about 1–3%) and the loosely bound bioavailablefraction can act on your body. That's why two men with the same total testosterone can feel completely different: if one has high SHBG, far less of his testosterone is usable.
The Vermeulen equation estimates these fractions from total T, SHBG, and albumin and tracks closely with the gold-standard equilibrium-dialysis lab method — which is why it's widely used clinically. New to the markers? Read free vs total testosterone.
No lab results yet? Start with the 2-minute Testosterone Symptom Check to see whether your symptoms are worth discussing with a doctor.
Frequently asked questions
What is free testosterone?+
Free testosterone is the small fraction (~1–3%) of total testosterone not bound to proteins (SHBG and albumin), so it's freely available to your tissues. Because SHBG varies between people, two men with identical total testosterone can have very different free testosterone.
How is free testosterone calculated?+
This tool uses the Vermeulen equation — the clinical standard — which estimates free and bioavailable testosterone from total testosterone, SHBG, and albumin using their known binding constants. It closely tracks the gold-standard equilibrium dialysis method.
What is a normal free testosterone level?+
Typical adult-male free testosterone is roughly 5–21 ng/dL (about 50–210 pg/mL), though reference ranges vary by laboratory, assay, and age. Your lab's own range — and your symptoms — matter more than any single number.
What's the difference between free and bioavailable testosterone?+
Free testosterone is completely unbound. Bioavailable testosterone is the free portion plus the loosely albumin-bound portion — both are usable by the body. Bioavailable is typically 30–55% of total; free is around 1–3%.
Keep reading
This calculator is for general educational purposes only and is not medical advice, a diagnosis, or a substitute for professional care. Estimates use the Vermeulen equation and standard binding constants; results vary by laboratory, assay, and the constants used. If you have concerns about your hormone health, consult a licensed healthcare provider.