Free Testosterone Calculator (Vermeulen)

Calculate free testosterone from total testosterone and SHBG, and check against BSSM thresholds.

By Dr Amer Sheikh, GP Updated 17 October 2026 Clinical review pending

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BSSM thresholds

Result	Meaning
Total under 8 nmol/L or free under 0.180 nmol/L	Deficiency confirmed (with symptoms)
Total under 12 or free under 0.225	Possible deficiency
Total over 12 nmol/L	Normal

Taking the sample

Between 7 and 11 am, fasting if possible.
Confirm on a second sample, ideally 4 weeks apart.
Check LH, FSH and prolactin if low.

Frequently asked questions

How is free testosterone calculated?

With the Vermeulen equation, from total testosterone, SHBG and albumin.

What free testosterone is low?

Below 0.225 nmol/L suggests possible deficiency; below 0.180 confirms it in a man with symptoms.

When should testosterone be checked?

In the morning, fasting, on two occasions.

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References

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):3666–72.
British Society for Sexual Medicine. Guidelines on adult testosterone deficiency.

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