Free Testosterone Calculator
Estimate free and bioavailable testosterone from total testosterone, SHBG, and albumin lab values using the widely used Vermeulen equation.
What free testosterone means
Most testosterone in the blood is bound to proteins — mainly sex hormone-binding globulin (SHBG) and albumin — and is not biologically active. Free testosterone is the small unbound fraction available to act on tissues, and is often considered a more accurate reflection of hormonal status than total testosterone alone.
The formula used
This calculator uses the Vermeulen equation, a validated method that estimates free testosterone from total testosterone, SHBG, and albumin using known protein-binding association constants, solved as a quadratic equation.
Lab methods and reference ranges vary between labs and populations. This tool is for general educational purposes only and does not replace direct free testosterone assay results or interpretation by a qualified healthcare professional.