Estimate free testosterone using SHBG-based formulas, assess symptom burden, and prepare informed questions for your clinician.
Start Calculator →Use values from a recent blood panel. Leave optional fields blank if unavailable.
Educational estimate only. Discuss with a licensed clinician.
Important: This tool provides educational estimates only. It does not diagnose hypogonadism, recommend TRT, or replace a medical evaluation. All hormone therapy decisions should be made with a licensed clinician using complete lab work and medical history.
A comprehensive hormone evaluation typically includes the following tests. Your clinician will determine which panels are appropriate for your situation.
| Lab Test | What It Measures | Typical Unit |
|---|---|---|
| Total Testosterone | All testosterone in blood (bound + free) | ng/dL |
| Free Testosterone | Unbound, biologically active testosterone | pg/mL |
| SHBG | Sex hormone-binding globulin; affects bioavailability | nmol/L |
| Albumin | Serum protein; used in free testosterone calculation | g/dL |
| Estradiol (E2) | Primary estrogen; important during TRT monitoring | pg/mL |
| CBC / Hematocrit | Red blood cell count; monitored during TRT for erythrocytosis | % |
| Lipid Panel | Cholesterol and triglycerides; cardiovascular risk | mg/dL |
| CMP | Comprehensive metabolic panel; liver and kidney function | Various |
| PSA (men 40+) | Prostate-specific antigen; prostate health screening | ng/mL |
This example illustrates how the calculator interprets a typical set of values and why SHBG context matters in clinical interpretation.
Reported symptoms: Low energy, low libido, poor sleep quality, brain fog / poor concentration (4 of 8).
Estimated Free Testosterone: Using the Vermeulen approximation with these values yields an estimated free testosterone in the borderline-to-low range. Despite a total testosterone value that some panels may categorize as within the lower-normal range, the elevated SHBG of 45 nmol/L is binding a significant portion of circulating testosterone, substantially reducing the bioavailable fraction.
Why SHBG Matters Here: Two patients with identical total testosterone of 380 ng/dL — one with SHBG of 20 nmol/L and another with SHBG of 45 nmol/L — will have meaningfully different free testosterone levels. This scenario illustrates why total testosterone alone is an incomplete picture, and why free testosterone and SHBG should always be evaluated together.
Interpretation: This patient's moderate symptom burden (4 of 8) combined with a borderline free testosterone level and upper-range SHBG suggests this case may warrant thorough clinical evaluation — including a full hormone panel, symptom history review, and discussion of cardiovascular and lifestyle factors with a licensed clinician.
This tool is designed as an educational resource only. The free testosterone calculation uses a simplified Vermeulen-based approximation and should not be interpreted as equivalent to a clinical laboratory measurement. The gold standard for free testosterone measurement is equilibrium dialysis, which is performed in a clinical laboratory setting.
The symptom checklist in this tool is not a validated clinical instrument and is not intended to diagnose hypogonadism, androgen deficiency, or any medical condition. Many of the symptoms listed overlap significantly with other conditions including thyroid disorders, sleep apnea, depression, and metabolic dysfunction.
Reference ranges for testosterone vary between laboratories, assay methods, age groups, and clinical context. Values that appear low or high in this tool may be interpreted differently by your clinician based on your complete medical history and individual physiology.
This calculator does not recommend TRT, any dosage, any medication, or any specific course of treatment. All hormone therapy decisions require evaluation by a licensed medical professional.
Free testosterone refers to the fraction of testosterone in the bloodstream that is not bound to carrier proteins — primarily SHBG (sex hormone-binding globulin) or albumin. Only unbound, or "free," testosterone can cross cell membranes and activate androgen receptors in tissues including muscle, bone, brain, and the reproductive system.
Free testosterone typically represents just 1–3% of total testosterone in the blood. Because such a small fraction is biologically active, even modest changes in protein binding can have significant effects on how the body responds to circulating testosterone. This is why a free testosterone calculator that accounts for SHBG provides more clinically meaningful context than total testosterone alone.
Total testosterone measures all testosterone in the blood — both the fraction bound to transport proteins (SHBG and albumin) and the small unbound free fraction. Free testosterone measures only the biologically active, unbound portion that is immediately available to cells.
The distinction matters clinically because two individuals can have identical total testosterone values but very different free testosterone levels depending on SHBG concentration. A person with a total testosterone of 420 ng/dL and high SHBG of 65 nmol/L may have substantially lower free testosterone than someone with 360 ng/dL total and SHBG of 18 nmol/L. This is why many clinicians now evaluate total vs free testosterone together when assessing symptoms of low T — and why this TRT calculator includes SHBG in the estimation.
SHBG (sex hormone-binding globulin) is a glycoprotein produced primarily by the liver. It binds tightly to sex hormones — particularly testosterone and estradiol — serving as a transport protein in the bloodstream. Testosterone bound to SHBG is essentially inert: it cannot enter cells or activate androgen receptors.
SHBG levels are influenced by many factors: age (SHBG tends to increase with aging), body weight, thyroid function, insulin sensitivity, liver health, and certain medications. Elevated SHBG effectively reduces bioavailable testosterone even when total testosterone appears normal. This is why the SHBG calculator component of this tool is central to estimating free testosterone, and why clinicians increasingly include SHBG testing in a thorough hormone panel. Addressing SHBG is often a critical component of testosterone optimization.
The symptoms most commonly associated with low testosterone include persistent fatigue and low energy, decreased libido, brain fog or difficulty concentrating, depressed or low mood, reduced muscle mass and strength, increased abdominal body fat, poor sleep quality, and reduced morning erections.
It is important to recognize that these low testosterone symptoms are non-specific — they overlap significantly with many other conditions including thyroid disorders, sleep apnea, depression, nutritional deficiencies, and metabolic dysfunction. Symptom burden should always be evaluated alongside comprehensive lab work and clinical history. The symptom scoring in this tool is for educational orientation only and does not constitute a clinical assessment or diagnosis.
Before initiating testosterone replacement therapy, a thorough clinician will typically order a comprehensive baseline panel that includes: total testosterone (ideally measured in the morning when levels peak), free testosterone, SHBG, albumin, estradiol (E2), complete blood count (CBC) with hematocrit, a comprehensive metabolic panel (CMP) for liver and kidney function, lipid panel, and PSA (prostate-specific antigen) for men aged 40 and older.
Some clinicians also evaluate LH (luteinizing hormone) and FSH (follicle-stimulating hormone) to distinguish primary from secondary hypogonadism, as well as prolactin, thyroid-stimulating hormone (TSH), and cortisol in certain clinical presentations. This baseline panel establishes reference values for ongoing monitoring and safety assessment during treatment.
Ongoing monitoring during testosterone replacement therapy is essential for safety and efficacy. Key parameters include: hematocrit and hemoglobin (TRT stimulates red blood cell production; elevated hematocrit increases cardiovascular risk), estradiol levels (testosterone aromatizes to estradiol; elevated E2 may cause fluid retention, mood changes, or other side effects), PSA (for prostate health surveillance), lipid panel (testosterone can affect cholesterol profiles), and testosterone trough or peak levels to confirm therapeutic range.
Monitoring frequency varies by protocol and clinician, but typically occurs at 3 months, 6 months, and then annually once stable values are established. Consistent lab tracking is a cornerstone of responsible testosterone optimization and long-term TRT management. Discuss your specific monitoring schedule with your prescribing clinician.
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