HEALTH CALCULATORS
Free Testosterone Calculator
Estimate your free and bioavailable testosterone from your total testosterone, SHBG, and albumin, using the validated Vermeulen equation.
Calculate Your Free Testosterone
Enter the values from your lab report.
Calculated with the Vermeulen equation. Reference ranges vary by lab, so compare your result with the range printed on your lab report and review it with your Provider.
For educational purposes only. This calculator does not diagnose any condition or replace an evaluation by a licensed healthcare Provider. Always review your results with your Provider.
What Is Free Testosterone?
Most of the testosterone in your blood is bound to proteins. A large share is tightly bound to sex hormone-binding globulin (SHBG), and most of the rest is loosely bound to albumin. Only a small fraction, usually around 1–3%, circulates freely. Free testosterone, along with the albumin-bound portion, makes up your bioavailable testosterone: the testosterone your tissues can actually use.
That’s why a total testosterone number alone doesn’t always tell the whole story. Two men with the same total testosterone can have very different free testosterone levels if their SHBG is different.
How This Calculator Works
This calculator uses the Vermeulen equation, the most widely used and validated method for estimating free testosterone from total testosterone, SHBG, and albumin. It models how testosterone binds to SHBG and albumin using published binding constants, and its results correlate closely with equilibrium dialysis, the laboratory gold standard for measuring free testosterone directly.
Important to Know
- Reference ranges for free testosterone vary from lab to lab. Compare your result with the range on your own lab report.
- A single number is never a diagnosis. Low testosterone is diagnosed using your symptoms, a physical exam, and properly timed lab work.
- Calculated free testosterone is an estimate. Directly measured free testosterone by equilibrium dialysis may differ slightly.
FAQ
Free Testosterone Questions.
Why does SHBG matter?
SHBG binds testosterone tightly, making it unavailable to your tissues. High SHBG can lower your free testosterone even when total testosterone looks normal, while low SHBG can do the opposite.
Is calculated free testosterone accurate?
The Vermeulen calculation correlates very closely with equilibrium dialysis, the gold-standard laboratory method, and is widely used in clinical practice and research.
What if I don’t have an albumin result?
Leave the standard value of 4.3 g/dL. Albumin has a relatively small effect on the result for most healthy men.
KNOW YOUR NUMBERS
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Source: Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999;84(10):3666–3672.