Calculate your free testosterone
Free testosterone from your total testosterone, SHBG and albumin — using the scientific Vermeulen equation.
Free testosterone calculator
Free testosterone calculator
Enter your values — you will find them on your lab report. Everything is calculated in your browser and never leaves your device.
Compare these values with the reference ranges on your own lab report.
This calculation uses the Vermeulen equation (1999) and is intended for education, not medical diagnosis. Reference ranges vary by laboratory. Always discuss your results with your doctor.
What is free testosterone?
Most of your testosterone is bound to proteins (mainly SHBG and albumin). Only the free and albumin-bound fraction is biologically active. Free testosterone therefore often gives a fuller picture than total testosterone.
How is it calculated?
This tool uses the Vermeulen equation: a validated method that estimates free testosterone from total testosterone, SHBG and albumin using known binding constants.
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Frequently asked questions
Which values do I need?
You need total testosterone and SHBG (both in nmol/L). Albumin is optional; if you leave it blank, we use the average value of 43 g/L.
What is the Vermeulen equation?
The Vermeulen equation (1999) estimates free testosterone from total testosterone, SHBG and albumin. It correlates well with the gold standard (equilibrium dialysis) and is widely used in endocrinology.
Which units should I use?
Total testosterone and SHBG in nmol/L, albumin in g/L — the units used by European laboratories. The correct unit is shown next to each field.
Are my entered values stored?
No. The calculation happens entirely in your browser: your entered values never leave your device and are not stored anywhere.
Is this the same as a lab measurement?
It is an estimate based on a formula, not a direct measurement. An exact value requires a laboratory assay. Discuss any abnormal results with your doctor.
Want your testosterone measured?
A blood test measures your total testosterone, SHBG and more — so you know your free testosterone accurately.