Four physician-built tools in one place: calculate your free testosterone with the Vermeulen formula, check your level against age-matched reference ranges, screen for low-T symptoms, and convert estradiol units. No login. No email required.
Adult male total testosterone reference range: typically 300-1000 ng/dL, with the optimal target depending on age. Free T (Vermeulen calculation) is often more clinically relevant, since it represents the bioavailable hormone after SHBG binding. Symptoms of low T (low energy, libido, mood, sleep quality) screened with the ADAM questionnaire correlate with biochemical low-T at total T below ~400 ng/dL.
Sources: Vermeulen A et al. JCEM 1999 · Endocrine Society Clinical Practice GuidelinesTotal testosterone tells you how much hormone is circulating, but only free and bioavailable testosterone is what your body can actually use. Enter your lab values to calculate both, using the same Vermeulen et al. (1999) formula clinicians rely on.
"Normal" depends on your age. Testosterone naturally declines about 1-2% per year after age 30. Enter your age and total testosterone to see where you fall within the age-matched reference range, and whether your level is in the optimal zone.
The ADAM (Androgen Deficiency in Aging Males) questionnaire is a 10-question screener developed at Saint Louis University and validated in clinical practice. Answer honestly, your responses stay on this device.
U.S. labs report estradiol in pg/mL; many international labs use pmol/L. Convert between units instantly, and if you enter your total testosterone, we'll compute your T:E2 ratio, a key marker for men on TRT.
Testosterone is one piece of the system. These tools fill in the rest, body composition, longevity, and the metabolic machinery that supports hormone optimization.
Hand-picked guides from our physician-edited library covering every angle of testosterone optimization, free T, SHBG, and estrogen management.
Each of the four tools above answers a different question men have about testosterone, and together they give you a far more useful picture than any single number on a lab report. Here's what each one is doing under the hood and how to interpret the output.
Most of the testosterone in your blood is bound to two proteins, about 60% to SHBG (sex hormone-binding globulin) and ~38% to albumin. Only ~1-3% floats freely, and only the free + albumin-bound fraction (called bioavailable testosterone) can interact with your tissues. The Vermeulen formula uses your total T, SHBG, and albumin to back-calculate this active fraction. Free T is the most important number when total T looks "normal" but you still feel symptomatic, high SHBG can leave plenty of total T while choking off the usable fraction.
Testosterone declines roughly 1-2% per year after age 30, so a "normal" level for a 25-year-old is very different from a "normal" level for a 55-year-old. Most reference labs (LabCorp, Quest) use age-stratified ranges that span roughly 240-950 ng/dL at age 20-29 and drop to 130-600 by age 70+. We compare your number to the age-matched range and also flag whether you're in the optimal zone (600-900 ng/dL), which corresponds to symptom-free physiology in most men, not just statistical normality.
The ADAM questionnaire was developed by John Morley at Saint Louis University and is one of the most widely used low-T screeners in primary care. The scoring rule is intentionally sensitive: a "yes" to question 1 (libido) or 7 (erection quality), or a "yes" to any 3 of the remaining 8 questions, flags a positive screen. ADAM is not diagnostic, it tells you whether the cluster of symptoms you're experiencing is consistent with what guys with biochemically confirmed low T report. A positive screen plus a morning total T below 300 ng/dL is the standard threshold for diagnosis.
Two reasons men care about estradiol: (1) U.S. labs report E2 in pg/mL while EU/UK/AU labs use pmol/L, and (2) men on TRT need to monitor it because exogenous testosterone gets aromatized into estradiol. Too low (<15 pg/mL) and you'll feel joint pain, low libido, and low mood; too high (>50 pg/mL) and you risk water retention, gyno, and emotional volatility. The T:E2 ratio (T in ng/dL ÷ E2 in pg/mL) above ~10 is generally considered favorable.
Yes, it's been validated against the gold standard (equilibrium dialysis) in multiple studies and is the formula recommended by the International Society for the Study of the Aging Male and most endocrinology societies. The two main alternatives, direct free T immunoassay and Tru-T, have known accuracy issues in the typical clinical range. Calculated free T using Vermeulen is what most experienced TRT physicians use.
Most lab reference ranges put the bottom of "normal" around 5 ng/dL (50 pg/mL). Most TRT physicians target 15-25 ng/dL (150-250 pg/mL) for symptom resolution. Below 6.5 ng/dL is generally considered hypogonadal regardless of total T.
Use the calculator. Direct free T immunoassays, what most U.S. labs run by default, are notoriously unreliable in the normal-range. Order total testosterone + SHBG + albumin (sometimes called a "free + total testosterone, calculated" panel), then plug those into the Vermeulen calculator. That's what your endocrinologist will do anyway.
It means your symptom pattern is consistent with low testosterone, but ADAM is highly sensitive and not very specific, so plenty of men screen positive without low T (depression, sleep apnea, and thyroid issues all overlap). A positive screen is a green light to get a morning total T blood draw, not a diagnosis on its own.
Baseline draw should be done before 10 AM on two separate days at least a week apart (testosterone is diurnal and fluctuates). On TRT, most physicians recheck at 6 weeks after dose change, then every 3-6 months once stable, including total T, free T, E2 sensitive, hematocrit, and SHBG.
Testosterone Cypionate (TRT) directly replaces what your body isn't producing, fast, predictable, the gold standard for men with primary hypogonadism or who are done having children. Enclomiphene tells your testes to produce more on their own, preserves fertility, exits cleanly, ideal for younger men or those still planning a family. OPTML providers help you choose based on goals, age, and labs.
How this tool calculates
Testosterone levels are interpreted against the harmonized adult-male reference ranges published by Travison et al. (J Clin Endocrinol Metab 2017) and the Endocrine Society Clinical Practice Guideline for testosterone therapy. The tool flags values below the age-adjusted reference range and provides educational context.
Peer-reviewed sources
Important. This tool is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment. The tool does not prescribe medication, recommend specific dosing, or substitute for clinical evaluation. Compounded medications referenced anywhere on this site are not FDA-approved; the FDA does not verify the safety, effectiveness, or quality of compounded drugs. Treatment decisions are made only by a licensed U.S. physician after individual patient evaluation.