Free Testosterone Calculator

Enter your Total Testosterone, SHBG, and Albumin levels to calculate your Free Testosterone and Bioavailable Testosterone. The Free Testosterone Calculator uses the Vermeulen equation to estimate the biologically active fractions that total testosterone alone doesn't reveal — select your preferred units for each biomarker and get your results broken down instantly.

Enter your total serum testosterone value.

nmol/L

Sex hormone-binding globulin in nmol/L.

Serum albumin level. Standard value is ~4.3 g/dL.

Results

Free Testosterone

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Free Testosterone

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Free Testosterone (%)

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Bioavailable Testosterone

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Bioavailable Testosterone

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Bioavailable Testosterone (%)

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Testosterone Fractions Breakdown

Frequently Asked Questions

What is free testosterone and why does it matter?

Free testosterone is the small fraction (roughly 2–3%) of total testosterone that is not bound to any protein and is immediately available to cells. It is considered the most biologically active form, making it a more accurate indicator of androgenic activity than total testosterone alone.

What is the difference between free and bioavailable testosterone?

Free testosterone is entirely unbound, while bioavailable testosterone includes both the free fraction and the portion weakly bound to albumin. The albumin-bound fraction can easily dissociate and become available to tissues, so both are biologically relevant. SHBG-bound testosterone, by contrast, is biologically inactive.

What equation does this calculator use?

This calculator uses the Vermeulen equation (published in JCEM, 1999), which is widely regarded as the gold standard for estimating free testosterone from total testosterone, SHBG, and albumin without requiring an equilibrium dialysis measurement.

What are normal free testosterone levels?

Normal free testosterone ranges vary by age and sex. For adult males, typical ranges are approximately 5–21 ng/dL (174–729 pmol/L). For adult females, normal levels are much lower, around 0.1–0.85 ng/dL. Always compare results with your laboratory's reference ranges and consult a healthcare professional.

Do I need to enter my actual albumin level?

If you don't have a measured albumin value, you can use the standard default of 4.3 g/dL, which is the population mean used in most clinical equations. Albumin levels are relatively stable and do not vary greatly between healthy adults.

Why do different units affect the result?

Testosterone can be reported in ng/dL, ng/mL, or nmol/L depending on the laboratory. The calculator converts your input to nmol/L internally before applying the Vermeulen equation, so selecting the correct units for your lab report is essential for an accurate result.

Can I use this calculator for female hormone assessment?

Yes. The Vermeulen equation applies to both males and females. Testosterone levels in women are significantly lower, so ensure you enter the correct value and units. As always, results should be interpreted alongside a clinical consultation rather than in isolation.

Should I rely solely on this calculator for medical decisions?

No. This calculator is intended for informational and educational purposes only. The results are mathematical estimates and do not replace a diagnosis or treatment recommendation from a qualified healthcare professional. Always consult your doctor before making any health-related decisions.

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