Free Testosterone Calculator
Use this free testosterone calculator to estimate your free and bioavailable testosterone from total testosterone, SHBG, and albumin.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Free Testosterone Is Calculated
Only a small fraction of the testosterone circulating in blood, roughly 1 to 3%, is actually free and biologically active. The rest is bound to SHBG (sex hormone-binding globulin) and, more loosely, to albumin. Most standard lab panels report only total testosterone, which can be misleading on its own, since two people with the same total testosterone can have very different free testosterone if their SHBG levels differ¹.
What This Calculator Measures
This calculates free and bioavailable testosterone from three lab values, rather than requiring the more expensive direct measurement method. Bioavailable testosterone includes the free fraction plus the weakly albumin-bound portion, since that bound fraction is still physiologically available to tissues.
The Formula
The Vermeulen equation solves for free testosterone using the law of mass action and the experimentally-derived binding association constants between testosterone and albumin, and testosterone and SHBG¹. This requires a quadratic solve, not simple algebra.
Bioavailable testosterone = free testosterone + albumin-bound testosterone
How This Calculator Computes Your Result
Enter your total testosterone, SHBG, and albumin if you have it. If albumin isn't entered, a default of 4.3 g/dL, a commonly used population average, is applied and clearly labeled as a default rather than your actual value.
Why Calculated Free Testosterone Is Often Preferred Over Direct Assays
This isn't just a cost-driven workaround. An Endocrine Society position statement reviewing testosterone measurement methods found that direct analog immunoassays, a cheaper, faster lab method some panels use, showed genuinely poor reliability: the same sample measured by the same method at different laboratories varied by a coefficient of variation of 13 to 32%, and results for the identical sample using the identical method varied 2- to 6-fold between runs².
Equilibrium dialysis remains the true gold standard, but it's expensive and not widely available, which is why a well-validated calculation like Vermeulen's is generally considered more trustworthy than a cheap direct assay, not just a more convenient substitute for one².
A Note on Accuracy
This is a calculated estimate, not a direct measurement. Equilibrium dialysis is the actual gold standard for free testosterone; the Vermeulen calculation is a well-validated stand-in used because direct measurement is expensive and not widely available.
Frequently Asked Questions
Why calculate free testosterone instead of just using total testosterone?
Most lab panels report only total testosterone, even though the free fraction is what's biologically active, most testosterone in blood is bound to SHBG or albumin and isn't available to tissues¹.
How accurate is the calculated value?
Equilibrium dialysis is the actual gold standard, this calculation is a well-validated stand-in. Direct analog immunoassay free testosterone tests, a different and cheaper lab method some panels report, are known to be substantially less reliable, with documented variability as high as 2- to 6-fold between runs of the same sample².
What if I don't have my albumin value?
The calculator defaults to 4.3 g/dL, a commonly used population average, this is clearly a default, not your actual measured value, so entering your own result if you have it will be more accurate.
Is a low or high result diagnostic on its own?
No. Testosterone levels are interpreted alongside symptoms and a full clinical picture, not a single number in isolation.
Sources
A Critical Evaluation of Simple Methods for the Estimation of Free Testosterone in Serum, Vermeulen, Verdonck & Kaufman, Journal of Clinical Endocrinology & Metabolism, 1999
Utility, Limitations, and Pitfalls in Measuring Testosterone: An Endocrine Society Position Statement, Rosner et al., Journal of Clinical Endocrinology & Metabolism, 2007
Free Testosterone Calculator
Use this free testosterone calculator to estimate your free and bioavailable testosterone from total testosterone, SHBG, and albumin.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Free Testosterone Is Calculated
Only a small fraction of the testosterone circulating in blood, roughly 1 to 3%, is actually free and biologically active. The rest is bound to SHBG (sex hormone-binding globulin) and, more loosely, to albumin. Most standard lab panels report only total testosterone, which can be misleading on its own, since two people with the same total testosterone can have very different free testosterone if their SHBG levels differ¹.
What This Calculator Measures
This calculates free and bioavailable testosterone from three lab values, rather than requiring the more expensive direct measurement method. Bioavailable testosterone includes the free fraction plus the weakly albumin-bound portion, since that bound fraction is still physiologically available to tissues.
The Formula
The Vermeulen equation solves for free testosterone using the law of mass action and the experimentally-derived binding association constants between testosterone and albumin, and testosterone and SHBG¹. This requires a quadratic solve, not simple algebra.
Bioavailable testosterone = free testosterone + albumin-bound testosterone
How This Calculator Computes Your Result
Enter your total testosterone, SHBG, and albumin if you have it. If albumin isn't entered, a default of 4.3 g/dL, a commonly used population average, is applied and clearly labeled as a default rather than your actual value.
Why Calculated Free Testosterone Is Often Preferred Over Direct Assays
This isn't just a cost-driven workaround. An Endocrine Society position statement reviewing testosterone measurement methods found that direct analog immunoassays, a cheaper, faster lab method some panels use, showed genuinely poor reliability: the same sample measured by the same method at different laboratories varied by a coefficient of variation of 13 to 32%, and results for the identical sample using the identical method varied 2- to 6-fold between runs².
Equilibrium dialysis remains the true gold standard, but it's expensive and not widely available, which is why a well-validated calculation like Vermeulen's is generally considered more trustworthy than a cheap direct assay, not just a more convenient substitute for one².
A Note on Accuracy
This is a calculated estimate, not a direct measurement. Equilibrium dialysis is the actual gold standard for free testosterone; the Vermeulen calculation is a well-validated stand-in used because direct measurement is expensive and not widely available.
Frequently Asked Questions
Why calculate free testosterone instead of just using total testosterone?
Most lab panels report only total testosterone, even though the free fraction is what's biologically active, most testosterone in blood is bound to SHBG or albumin and isn't available to tissues¹.
How accurate is the calculated value?
Equilibrium dialysis is the actual gold standard, this calculation is a well-validated stand-in. Direct analog immunoassay free testosterone tests, a different and cheaper lab method some panels report, are known to be substantially less reliable, with documented variability as high as 2- to 6-fold between runs of the same sample².
What if I don't have my albumin value?
The calculator defaults to 4.3 g/dL, a commonly used population average, this is clearly a default, not your actual measured value, so entering your own result if you have it will be more accurate.
Is a low or high result diagnostic on its own?
No. Testosterone levels are interpreted alongside symptoms and a full clinical picture, not a single number in isolation.
Sources
A Critical Evaluation of Simple Methods for the Estimation of Free Testosterone in Serum, Vermeulen, Verdonck & Kaufman, Journal of Clinical Endocrinology & Metabolism, 1999
Utility, Limitations, and Pitfalls in Measuring Testosterone: An Endocrine Society Position Statement, Rosner et al., Journal of Clinical Endocrinology & Metabolism, 2007
Free Testosterone Calculator
Use this free testosterone calculator to estimate your free and bioavailable testosterone from total testosterone, SHBG, and albumin.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Free Testosterone Is Calculated
Only a small fraction of the testosterone circulating in blood, roughly 1 to 3%, is actually free and biologically active. The rest is bound to SHBG (sex hormone-binding globulin) and, more loosely, to albumin. Most standard lab panels report only total testosterone, which can be misleading on its own, since two people with the same total testosterone can have very different free testosterone if their SHBG levels differ¹.
What This Calculator Measures
This calculates free and bioavailable testosterone from three lab values, rather than requiring the more expensive direct measurement method. Bioavailable testosterone includes the free fraction plus the weakly albumin-bound portion, since that bound fraction is still physiologically available to tissues.
The Formula
The Vermeulen equation solves for free testosterone using the law of mass action and the experimentally-derived binding association constants between testosterone and albumin, and testosterone and SHBG¹. This requires a quadratic solve, not simple algebra.
Bioavailable testosterone = free testosterone + albumin-bound testosterone
How This Calculator Computes Your Result
Enter your total testosterone, SHBG, and albumin if you have it. If albumin isn't entered, a default of 4.3 g/dL, a commonly used population average, is applied and clearly labeled as a default rather than your actual value.
Why Calculated Free Testosterone Is Often Preferred Over Direct Assays
This isn't just a cost-driven workaround. An Endocrine Society position statement reviewing testosterone measurement methods found that direct analog immunoassays, a cheaper, faster lab method some panels use, showed genuinely poor reliability: the same sample measured by the same method at different laboratories varied by a coefficient of variation of 13 to 32%, and results for the identical sample using the identical method varied 2- to 6-fold between runs².
Equilibrium dialysis remains the true gold standard, but it's expensive and not widely available, which is why a well-validated calculation like Vermeulen's is generally considered more trustworthy than a cheap direct assay, not just a more convenient substitute for one².
A Note on Accuracy
This is a calculated estimate, not a direct measurement. Equilibrium dialysis is the actual gold standard for free testosterone; the Vermeulen calculation is a well-validated stand-in used because direct measurement is expensive and not widely available.
Frequently Asked Questions
Why calculate free testosterone instead of just using total testosterone?
Most lab panels report only total testosterone, even though the free fraction is what's biologically active, most testosterone in blood is bound to SHBG or albumin and isn't available to tissues¹.
How accurate is the calculated value?
Equilibrium dialysis is the actual gold standard, this calculation is a well-validated stand-in. Direct analog immunoassay free testosterone tests, a different and cheaper lab method some panels report, are known to be substantially less reliable, with documented variability as high as 2- to 6-fold between runs of the same sample².
What if I don't have my albumin value?
The calculator defaults to 4.3 g/dL, a commonly used population average, this is clearly a default, not your actual measured value, so entering your own result if you have it will be more accurate.
Is a low or high result diagnostic on its own?
No. Testosterone levels are interpreted alongside symptoms and a full clinical picture, not a single number in isolation.
Sources
A Critical Evaluation of Simple Methods for the Estimation of Free Testosterone in Serum, Vermeulen, Verdonck & Kaufman, Journal of Clinical Endocrinology & Metabolism, 1999
Utility, Limitations, and Pitfalls in Measuring Testosterone: An Endocrine Society Position Statement, Rosner et al., Journal of Clinical Endocrinology & Metabolism, 2007