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Free testosterone calculator

Estimate the free and bioavailable share of testosterone from a total testosterone result, SHBG and albumin, using the Vermeulen equation.

Calculate free and bioavailable testosterone

Enter results from the same blood draw. Albumin is set to a common value of 4.3 g/dL, and you can replace it with the number on your report. This is an estimate, not a diagnosis.

Blood test results

Use the unit printed on your lab report. Morning samples are preferred.

SHBG is sex hormone binding globulin. Use the result from the same blood draw. A reliable SHBG is needed for a useful estimate.

Leave this at 4.3 if your report does not give albumin. Use the lab value when you have it.

Your result

Enter total testosterone and SHBG to see free testosterone, bioavailable testosterone and the approximate reference band. Albumin defaults to 4.3 g/dL.

This tool is for adult men. It does not cover women, transgender hormone therapy, teenagers or bodybuilding cycles.

Warning signs that need prompt care

Do not use this calculator to decide whether symptoms are urgent.

  • An erection that lasts more than 4 hours. A persistent, painful erection is a medical emergency and needs prompt assessment (Shigehara and Namiki).
  • Chest pain with sexual activity. Chest pain, pressure or breathlessness during sexual activity needs urgent medical assessment. Erectile dysfunction can also be linked to heart and blood vessel disease (Yafi et al.).
  • A breast lump or breast swelling in a man. New breast tissue, a lump or one-sided swelling needs a doctor's review (Sansone et al.).
  • A testicular lump. A new lump or swelling in the testicle needs prompt assessment (Baird et al.).
  • Sudden loss of libido with headaches or vision change. This combination needs prompt medical assessment.
  • Low mood with thoughts of self-harm. Get immediate help. In the US, call or text 988 for the Suicide and Crisis Lifeline.

If you are unsure, call your doctor or emergency services.

How the calculator works

Free testosterone is the small part of testosterone not bound to SHBG or albumin. Free testosterone plus albumin-bound testosterone is called bioavailable testosterone. In healthy men, free testosterone is about 2 percent of total testosterone.7 The calculator uses the binding equation published by Vermeulen, Verdonck and Kaufman, the approach used in many clinical laboratories.1, 15

T = total testosterone in mol/L

S = SHBG in mol/L

A = albumin in mol/L

N = 1 + Ka x A

a = N x Kt

b = N + Kt x (S - T)

c = -T

free T = (-b + square root of (b squared - 4ac)) / (2a)

bioavailable T = free T x N

Kt is 1.0 x 109 L/mol for SHBG and Ka is 3.6 x 104 L/mol for albumin. Albumin in mol/L is albumin in g/dL x 10 / 66,430. Total testosterone in nmol/L is multiplied by 10-9. SHBG in nmol/L is multiplied by 10-9. To convert ng/dL to nmol/L, divide by 28.84. Free testosterone in pg/mL is free testosterone in nmol/L x 288.4.

Worked example: total testosterone 15 nmol/L (about 433 ng/dL), SHBG 40 nmol/L and albumin 4.3 g/dL. T = 15 x 10-9 mol/L, S = 40 x 10-9 mol/L, and A = 4.3 x 10 / 66,430 = 6.47 x 10-4 mol/L. N = 1 + 3.6 x 104 x 6.47 x 10-4 = 24.30. Then a = 24.30 x 109, b = 49.30 and c = -15 x 10-9. The positive root gives free T = 0.269 nmol/L, or 77.5 pg/mL and 1.79 percent of total. Bioavailable testosterone is 0.269 x 24.30 = 6.53 nmol/L, about 188 ng/dL. These values match the calculator.

How to read the result

The result shows free testosterone in pg/mL and pmol/L, its percentage of total, and bioavailable testosterone. The band is an approximate guide, not a diagnosis. Reference intervals differ by lab, assay and age. This tool uses the all-men interval from a standardized equilibrium dialysis study, 66 to 309 pg/mL (229 to 1,072 pmol/L).5 A study using the Vermeulen equation in younger men reported 0.245 to 0.785 nmol/L, about 71 to 226 pg/mL.7 Your lab's range matters.

A below-band result can reflect low total testosterone, high SHBG, lab variation or both. It does not prove deficiency. Talk to a doctor if you also have low sex drive, fatigue, loss of muscle or low mood. See our guides to low testosterone symptoms in men over 50 and causes of low testosterone in men. Within the band does not rule out symptoms. Above the band can reflect high total testosterone, low SHBG, assay variation or testosterone medicine. Do not start, stop or change a prescription on your own.

Low testosterone is diagnosed with symptoms and signs plus two early-morning blood tests, not from symptoms alone.2, 3 The Endocrine Society recommends morning fasting total testosterone and a repeat measurement, and free testosterone when total testosterone is near the lower limit or SHBG is altered.2 A calculated free testosterone needs a reliable SHBG and a morning sample, and a doctor interprets it with your symptoms. See our guide to normal testosterone levels by age.

What free T can and cannot tell you

SHBG binds testosterone. High SHBG lowers free testosterone even when total testosterone is normal; low SHBG can keep free testosterone normal when total testosterone is low. SHBG changes with age, body weight, liver disease, thyroid disease, diabetes and some medicines.2, 14 That is why free testosterone can help when total testosterone is borderline or SHBG is abnormal, and why it can mislead when SHBG is unreliable. See free vs total testosterone.

The calculation is not a measurement. The equation assumes fixed binding constants and a consistent albumin concentration. Calculated free testosterone was close to equilibrium dialysis in the original validation except during pregnancy.1 Later work found different equations can differ substantially, with mean differences up to 56 percent.7 A review also found the assumptions behind common binding models are not fully supported by experimental data.14 Use the result as an estimate. If your lab reports albumin, enter it; very low or very high albumin makes the estimate less reliable. Morning samples matter because testosterone is higher then.2 Total testosterone also falls with age.6 See what testosterone is.

What to bring to a doctor

Bring the lab report with total testosterone, SHBG and albumin, including units and the date and time of the draw. Bring earlier results, your symptoms and a list of medicines and supplements. Mention conditions that affect SHBG or testosterone. Our guide to the testosterone blood test explains the test. The ADAM low testosterone quiz can help you note symptoms, but it is not a diagnosis.

Testosterone replacement therapy comes as gels, injections, pellets and other prescription forms. It is used for men with confirmed hypogonadism and can suppress sperm production, so it is not a fertility treatment.2, 8 In TRAVERSE, testosterone gel was noninferior to placebo for major cardiovascular events, but atrial fibrillation, acute kidney injury and pulmonary embolism were more common.4 Whether it is appropriate is a decision for a doctor; see our guide to testosterone replacement therapy.

Erectile dysfunction can be an early sign of heart and blood vessel disease and diabetes, and it is a reason to see a doctor.9, 10 This page makes no performance promises. For general steps, see increasing testosterone naturally after 50. For a neutral comparison of supplement labels and the evidence behind them, see our male vitality supplement comparison guide.

Frequently asked questions

Can this calculator diagnose low testosterone?

No. Diagnosis needs symptoms and signs plus two morning total testosterone measurements. A calculator cannot make it.2, 3

What is a normal free testosterone level?

There is no single number. This tool uses 66 to 309 pg/mL; another study found 0.245 to 0.785 nmol/L in younger men. Use your lab's range.5, 7

Does a high free T mean I need testosterone therapy?

No. It can reflect assay variation, high total testosterone, low SHBG or testosterone medicine. Therapy is a prescription decision for confirmed hypogonadism.2, 4

Can I use this calculator if I take testosterone?

It can give an estimate, but monitoring should follow your doctor's plan and the lab's methods. Do not change a prescription based on this calculator.2

Sources

  1. 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. PubMed PMID 10523012.
  2. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744. PubMed PMID 29562364.
  3. Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. J Urol. 2018;200(2):423-432. PubMed PMID 29601923.
  4. Lincoff AM, Bhasin S, Flevaris P, et al. Cardiovascular Safety of Testosterone-Replacement Therapy. N Engl J Med. 2023;389(2):107-117. PubMed PMID 37326322.
  5. Jasuja R, Pencina KM, Spencer DJ, et al. Reference intervals for free testosterone in adult men measured using a standardized equilibrium dialysis procedure. Andrology. 2023;11(1):125-133. PubMed PMID 36251328.
  6. Travison TG, Vesper HW, Orwoll E, et al. Harmonized Reference Ranges for Circulating Testosterone Levels in Men of Four Cohort Studies in the United States and Europe. J Clin Endocrinol Metab. 2017;102(4):1161-1173. PubMed PMID 28324103.
  7. Ho CK, Stoddart M, Walton M, Anderson RA, Beckett GJ. Calculated free testosterone in men: comparison of four equations and with free androgen index. Ann Clin Biochem. 2006;43(Pt 5):389-397. PubMed PMID 17036414.
  8. McBride JA, Coward RM. Recovery of spermatogenesis following testosterone replacement therapy or anabolic-androgenic steroid use. Asian J Androl. 2016;18(3):373-380. PubMed PMID 26908067.
  9. Yafi FA, Jenkins L, Albersen M, et al. Erectile dysfunction. Nat Rev Dis Primers. 2016;2:16003. PubMed PMID 27188339.
  10. Defeudis G, Mazzilli R, Tenuta M, et al. Erectile dysfunction and diabetes: A melting pot of circumstances and treatments. Diabetes Metab Res Rev. 2022;38(2):e3494. PubMed PMID 34514697.
  11. Shigehara K, Namiki M. Clinical Management of Priapism: A Review. World J Mens Health. 2016;34(1):1-8. PubMed PMID 27169123.
  12. Baird DC, Meyers GJ, Hu JS. Testicular Cancer: Diagnosis and Treatment. Am Fam Physician. 2018;97(4):261-268. PubMed PMID 29671528.
  13. Sansone A, Romanelli F, Sansone M, Lenzi A, Di Luigi L. Gynecomastia and hormones. Endocrine. 2017;55(1):37-44. PubMed PMID 27145756.
  14. Goldman AL, Bhasin S, Wu FCW, Krishna M, Matsumoto AM, Jasuja R. A Reappraisal of Testosterone's Binding in Circulation: Physiological and Clinical Implications. Endocr Rev. 2017;38(4):302-324. PubMed PMID 28673039.
  15. Chung MC, Gombar S, Shi RZ. Implementation of Automated Calculation of Free and Bioavailable Testosterone in Epic Beaker Laboratory Information System. J Pathol Inform. 2017;8:28. PubMed PMID 28828199.

This tool provides general health information, not a diagnosis or medical advice. A calculated free testosterone is an estimate. Talk with a healthcare professional about your result, your symptoms, and your care, especially if you take medication or have a medical condition.

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