Loading Calculator...
Please wait a moment
Please wait a moment
Calculate free and bioavailable testosterone from total testosterone, SHBG, and albumin. Assess for hypogonadism with age-specific reference ranges.
Age affects normal testosterone ranges
Male normal: 300-1000 ng/dL (varies by age)
Male normal: 10-57 nmol/L
Normal: 3.5-5.5 g/dL (default: 4.4 g/dL)
Hypogonadism requires both low testosterone AND symptoms
| Age Range | Total Testosterone | Free Testosterone |
|---|---|---|
| 20-29 years | 400-1080 ng/dL | 9-30 ng/dL |
| 30-39 years | 350-1000 ng/dL | 8-28 ng/dL |
| 40-49 years | 300-950 ng/dL | 7-25 ng/dL |
| 50-59 years | 280-900 ng/dL | 6-23 ng/dL |
| 60+ years | 250-850 ng/dL | 5-20 ng/dL |
Note: Ranges vary between laboratories. These are general reference ranges. Testosterone naturally declines ~1-2% per year after age 30.
Testosterone is the primary male sex hormone, essential for reproductive function, muscle mass, bone density, libido, mood, and overall well-being. It circulates in three forms: free (2-3%, biologically active), albumin-bound (40-50%, weakly bound and bioavailable), and SHBG-bound (40-50%, tightly bound and inactive).
Total Testosterone: Measures all three forms but doesn't reflect biologically active hormone. Can be misleading when SHBG is abnormal - high SHBG increases total T but decreases free T; low SHBG decreases total T but may increase free T.
Free Testosterone: The unbound, biologically active form that enters cells to exert effects. Most clinically relevant measurement. Can be directly measured (expensive, technically challenging) or calculated from total T, SHBG, and albumin (this calculator uses the validated Vermeulen equation).
Bioavailable Testosterone: Free plus albumin-bound testosterone, representing the fraction available to tissues. Albumin binding is weak and reversible, so this hormone can dissociate and become active.
Male hypogonadism (low testosterone) is diagnosed when testosterone levels are low AND clinical symptoms are present. Symptoms alone or low testosterone alone are insufficient for diagnosis. Primary hypogonadism results from testicular failure (elevated LH/FSH). Secondary hypogonadism results from pituitary/hypothalamic dysfunction (low or normal LH/FSH). Common causes include aging, obesity, medications (opioids, steroids), diabetes, chronic illness, and genetic disorders.
TRT can improve symptoms in men with confirmed hypogonadism. Benefits include increased libido, improved erectile function, increased muscle mass and strength, improved mood and energy, and increased bone density. However, risks include erythrocytosis (increased red blood cells), potential cardiovascular effects, decreased fertility, prostate concerns (TRT doesn't cause cancer but can stimulate existing cancer), and testicular atrophy. Regular monitoring of testosterone levels, hematocrit, PSA, and clinical response is essential.
Testing is indicated for symptoms of hypogonadism: decreased libido, erectile dysfunction, fatigue, decreased muscle mass, increased body fat, mood changes, or osteoporosis in men. Testing should be done with a morning (8-10 AM) blood sample when testosterone is highest. Two low measurements are required for diagnosis. Avoid testing during acute illness as stress temporarily lowers testosterone. In women, testosterone may be tested for signs of hyperandrogenism (hirsutism, virilization, PCOS).
Free testosterone represents the biologically active hormone that can enter cells and bind to androgen receptors. Total testosterone can be misleading because it includes hormone tightly bound to SHBG (inactive). Men with high SHBG (due to aging, liver disease, hyperthyroidism, or medications) may have normal total T but low free T and symptoms. Conversely, men with low SHBG (obesity, hypothyroidism, insulin resistance) may have low total T but normal free T without symptoms. Free testosterone better reflects true hormonal status.
SHBG increases with: aging, hyperthyroidism, liver disease, estrogen (including from obesity converting testosterone to estrogen), HIV infection, and medications like anticonvulsants. High SHBG decreases free testosterone availability. SHBG decreases with: obesity, insulin resistance/diabetes, hypothyroidism, growth hormone excess, nephrotic syndrome, and androgens. Low SHBG increases free testosterone proportion. Understanding SHBG is crucial for interpreting total testosterone levels accurately.
Primary hypogonadism (testicular failure) means the testes aren't producing testosterone despite adequate pituitary stimulation. LH and FSH are elevated trying to stimulate the testes. Causes include Klinefelter syndrome, chemotherapy, radiation, trauma, mumps orchitis, or aging. Secondary hypogonadism (hypothalamic-pituitary dysfunction) means the brain isn't sending signals to the testes. LH and FSH are low or inappropriately normal. Causes include pituitary tumors, medications (especially opioids), obesity, aging, or chronic illness. Treatment and fertility implications differ between types.
Current evidence does not support that TRT causes prostate cancer in men without pre-existing cancer. However, TRT can stimulate growth of existing prostate cancer (testosterone-dependent). Before starting TRT, prostate cancer screening with PSA and digital rectal exam is essential. TRT is contraindicated in men with known prostate cancer. During TRT, regular PSA monitoring is required. A rapid PSA rise warrants urological evaluation. The relationship between TRT and prostate cancer remains an area of ongoing research and monitoring.
Yes, particularly in men with modifiable risk factors. Weight loss in obese men can significantly increase testosterone (obesity causes insulin resistance which suppresses testosterone production and increases aromatase converting T to estrogen). Regular resistance exercise and adequate sleep improve testosterone levels. Reducing alcohol consumption helps. Stress reduction may help as chronic stress elevates cortisol which suppresses testosterone. Adequate vitamin D and zinc are important. However, lifestyle changes may not normalize severely low testosterone or address underlying pathology. They're important adjuncts but may not replace TRT when truly needed.
Regular monitoring is essential during TRT. Testosterone levels should be checked 3-6 months after starting therapy and annually thereafter (timing depends on formulation - trough for injections, anytime for gels/patches). Target is mid-normal range for age. Complete blood count monitors hematocrit (TRT increases RBC production; hematocrit > 54% requires dose adjustment or phlebotomy). PSA and prostate exam annually. Liver function tests. Bone density at baseline if osteoporosis risk. Lipid panel. Symptom assessment. Fertility evaluation if preservation desired (TRT suppresses sperm production).
Testosterone naturally declines about 1-2% per year after age 30 due to multiple factors. Testicular Leydig cells (which produce testosterone) decrease in number and function. LH secretion patterns change with less pulsatility. SHBG increases with age, binding more testosterone. Chronic conditions common with aging (obesity, diabetes, medications, sleep apnea) suppress testosterone. Increased aromatase activity converts more testosterone to estrogen. However, age-related decline is gradual and variable - many older men maintain normal levels. Low testosterone in older men often reflects reversible factors (medications, illness, obesity) rather than aging alone.
Assess PCOS diagnostic criteria
Interpret thyroid function tests
Assess cortisol and ACTH levels
Assess for adrenal insufficiency
Calculate body mass index
Assess vitamin D levels and dosing