Free testosterone calculator (Vermeulen equation)
Short answer: Only about 2% of testosterone in the blood is free; the rest is bound to SHBG and albumin. Free testosterone can be calculated from total testosterone, SHBG and albumin with the Vermeulen equation, which matches the lab’s reference method closely. In men, a calculated free testosterone below 220 pmol/L (about 6.3 ng/dL) is the level linked with low testosterone.
Free calculator
Free testosterone calculator (Vermeulen)
Free testosterone from total testosterone, SHBG and albumin (Vermeulen 1999)
Sources: 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.
ng/dL in the US, nmol/L in most other countries
In nmol/L
Leave empty to use a typical 4.3 g/dL (43 g/L)
Your result
Enter the numbers from your lab report to see your result.
Use total testosterone from a morning blood test (before 10 am), when it is highest. A calculated free testosterone is an estimate; it is close to the lab’s reference method in most people.
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A pointer, not a diagnosis. Talk to a doctor about your result, and sooner if you feel unwell.
How to read the result
- Below 220 pmol/L (6.3 ng/dL)< 220pmol/LFor a man, this is below the level a large European study used, together with a low total testosterone and symptoms, to define low testosterone. One number is not a diagnosis: testosterone dips with illness, poor sleep and hard dieting. A repeat morning test and a talk with a doctor are the next step.
- 220 pmol/L (6.3 ng/dL) or above≥ 220pmol/LFor a man, this is above the level linked with low testosterone. Compare it with the range your lab prints, which differs between labs.
Your lab’s range
Labs print their own free testosterone range, and they differ a lot: for adult men often about 170–700 pmol/L (roughly 50–200 pg/mL), for women a much lower range. Your lab’s range comes first. The 220 pmol/L line is the cut-off for low testosterone in men from the European Male Ageing Study, not a target.
How it is worked out
Free testosterone from total testosterone, SHBG and albumin (Vermeulen 1999)
Use total testosterone from a morning blood test (before 10 am), when it is highest. A calculated free testosterone is an estimate; it is close to the lab’s reference method in most people.
Sources
- 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.
- Wilke TJ, Utley DJ. Total testosterone, free-androgen index, calculated free testosterone, and free testosterone by analog RIA compared in hirsute women and in otherwise-normal women with altered binding of sex-hormone-binding globulin. Clin Chem 1987;33(8):1372-1375.
- Wu FCW, Tajar A, Beynon JM, et al. Identification of late-onset hypogonadism in middle-aged and elderly men. N Engl J Med 2010;363(2):123-135.
The markers it uses
Questions
- How is free testosterone calculated?
- From your total testosterone, SHBG and albumin, with the equation Vermeulen and colleagues published in 1999. It works out how much testosterone is bound to SHBG (tightly) and to albumin (loosely), and what is left free. If you have no albumin result, a typical 4.3 g/dL is used, which changes the answer very little.
- What is a normal free testosterone level for a man?
- Lab ranges differ, but for adult men they often run from about 170 to 700 pmol/L (about 50 to 200 pg/mL). The European Male Ageing Study used a calculated free testosterone below 220 pmol/L, together with a low total testosterone and symptoms, to define low testosterone.
- Why does SHBG matter?
- SHBG holds testosterone tightly, so the same total testosterone can mean less free testosterone when SHBG is high (common with age, a lean build, liver disease or an overactive thyroid) and more when it is low (common with extra weight and insulin resistance).
- What is the free androgen index (FAI)?
- 100 × total testosterone ÷ SHBG, both in nmol/L. It is mostly used for women, for example when checking for PCOS, because a calculated free testosterone is less reliable at low levels. In men it is a poor guide when SHBG is low, so the calculated free testosterone is the better number.
- Should I use this for a woman’s result?
- You can, and the calculator shows the numbers, but it does not judge the result for women: female ranges are low and differ between labs. Compare your free testosterone and free androgen index with the ranges your lab prints, and talk to a doctor about them.
A pointer, not a diagnosis. Talk to a doctor about your result, and sooner if you feel unwell. Reference ranges are general-population guidance compiled from common clinical laboratories, not a diagnosis. Lab-to-lab ranges differ. Always read your results with your doctor.