Your biological age is an estimate of how old your body actually is on the inside — which can be very different from the number of birthdays you have had. This free biological age calculator gives you two ways to find out. The Quick mode takes about 60 seconds and uses only your everyday habits, […]
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June 24, 2026
Free Testosterone Calculator: Estimate Bioavailable T & Model TRT
June 24, 2026
Free testosterone is the small, unbound fraction of your total testosterone that is actually available for your body to use — and it often tells a more useful story than total testosterone alone. This free testosterone calculator gives you two tools in one. The Free Testosterone tab estimates your bioavailable and free testosterone from a standard blood panel using the peer-reviewed Vermeulen method, while the TRT Simulator models how testosterone levels rise and settle on a given dosing schedule. Enter your numbers below, then see how comprehensive hormone testing can turn an estimate into a plan.
Longevity Centers of America
Testosterone Toolkit
Calculate your free testosterone, then model any TRT protocol.
Your Labs
most US labs report ng/dL
sex hormone binding globulin
leave blank to use the standard 4.3 g/dL
Enter total testosterone and SHBG (both greater than zero).
Free Testosterone
— ng/dL
—
Free T (% of total)
—
Free T (pg/mL)
—
Bioavailable T
Methodology & sources
Free and bioavailable testosterone are calculated from total testosterone, SHBG, and albumin using the equilibrium-binding equation of 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. Association constants: SHBG 1.0×10⁹ L/mol, albumin 3.6×10⁴ L/mol. If albumin is left blank, the standard 4.3 g/dL is used. Results depend on assay accuracy and may differ from equilibrium-dialysis measurement.
For educational and wellness reference only. This is a calculation from your entered values, not a diagnosis or medical advice. Reference ranges vary by laboratory, assay, and age. These statements have not been evaluated by the FDA. Consult a licensed healthcare provider to interpret your hormone levels.
Your Protocol
your natural level, if adding on top
Enter a dose, an injection interval, and weeks to simulate (all greater than zero).
Serum testosterone (modeled)
Steady-state window
—
Steady-state average
—
Peak → trough (ng/dL)
—
Peak : trough ratio
—
Time to ~95% steady state
—
Level stability
We Listen. We Test. We Heal.
A model is a guide, not a prescription. The right ester, dose, and frequency for you come from labs, symptoms, and a physician who actually listens.
Explore Hormone OptimizationMethodology & sources
A simplified one-compartment pharmacokinetic model. Each injection contributes a rise-and-decline curve (first-order absorption and elimination, summed by superposition); the ester’s published terminal half-life governs accumulation and the trough, and each ester is adjusted for the fraction of its weight that is actual testosterone. Half-lives used (days): propionate ~0.8, phenylpropionate ~1.5, isocaproate ~4, enanthate ~4.5, cypionate ~8, undecanoate ~21; Sustanon 250 is modeled as its four component esters. Absolute ng/dL values are population estimates calibrated to typical clinical response and will differ between individuals; the shape, peak-to-trough swing, and time-to-steady-state are the reliable, comparative outputs. Time to ~95% steady state ≈ 4.3 × terminal half-life.
For educational purposes only. This is a simplified pharmacokinetic model, not medical advice, a prescription, or a recommendation to use testosterone or any specific protocol. Testosterone is a controlled substance and must be prescribed and monitored by a licensed physician. Individual pharmacokinetics, absorption, and response vary widely. These statements have not been evaluated by the FDA. Consult a licensed healthcare provider before beginning or changing any therapy.
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Free Testosterone & TRT tools by Longevity Centers of America
How to Use the Free Testosterone Calculator
Pick the tool that matches your question. In the Free Testosterone tab, enter your total testosterone, your sex hormone binding globulin (SHBG), and either your albumin or a default value — the calculator applies the Vermeulen equation to estimate your free and bioavailable testosterone in seconds, along with the percentage of testosterone that is actually active. In the TRT Simulator tab, enter a dose, injection frequency, and ester half-life to model how your levels rise, peak, and reach steady state over the weeks following a protocol change, so you can see the difference between, say, weekly and twice-weekly dosing before discussing options with a clinician.
What Is Free Testosterone?
Most of the testosterone circulating in your blood is bound to proteins — tightly to SHBG and loosely to albumin — and is not directly available to your tissues. Free testosterone is the roughly one to two percent that travels unbound, and together with the albumin-bound portion it makes up your bioavailable testosterone. Because conditions like aging, obesity, and thyroid or liver changes can shift SHBG up or down, two people with an identical total testosterone can have very different amounts of usable hormone. That is why symptoms sometimes line up better with free testosterone than with the total number on a lab report.
The Science: The Vermeulen Method
The Free Testosterone tab is built on the Vermeulen calculation, a widely cited 1999 model that estimates free and bioavailable testosterone from total testosterone, SHBG, and albumin using the known binding affinities of those proteins. It has become a clinical standard because it tracks closely with the gold-standard equilibrium dialysis measurement while requiring only routine, inexpensive blood markers. The result is an estimate rather than a direct measurement, but for most people it is a far more informative figure than total testosterone considered on its own.
How to Support Healthy Testosterone
Many of the factors that shape testosterone are modifiable. Resistance training and adequate protein support hormone production, while consistent, sufficient sleep has a measurable effect on morning testosterone. Managing body composition matters too, since excess fat tissue increases the conversion of testosterone to estrogen and tends to lower SHBG. Limiting alcohol, managing chronic stress, and correcting deficiencies in nutrients such as vitamin D and zinc can all help. When lifestyle changes are not enough, a clinician can evaluate whether an underlying cause or a medically supervised therapy is appropriate.
Frequently Asked Questions
What is a free testosterone calculator? A free testosterone calculator estimates the unbound, usable fraction of your testosterone from a standard blood panel. This tool uses the validated Vermeulen method and also includes a simulator that models testosterone levels on a given TRT dosing schedule.
What labs do I need to calculate free testosterone? You need your total testosterone and your sex hormone binding globulin (SHBG). Albumin improves accuracy, but a standard default value can be used if you do not have it.
Why does free testosterone matter more than total testosterone? Most testosterone is bound to proteins and unavailable to your tissues. Free and bioavailable testosterone reflect the hormone your body can actually use, so they often line up better with symptoms than the total number.
How accurate is the Vermeulen calculation? The Vermeulen equation tracks closely with the gold-standard equilibrium dialysis measurement and is a recognized clinical standard. It produces an estimate from routine blood markers rather than a direct measurement.
Is this calculator medical advice? For educational and wellness purposes only. This calculator provides estimates from published models and lifestyle inputs, and is not a substitute for professional medical advice. Discuss your results with a qualified clinician.
Kyle Hulbert is the co-founder and operator at The Longevity Centers of America, which he built alongside Dr. Kosubevsky with the mission to drastically improve the lives of millions of people. Drawing on his own transformation as a patient, he designed the practice around accessibility, affordability, and focus on data-driven regenerative care for individuals who have been underserved by conventional medicine. His background bridges academic rigor and practical application. Hulbert holds bachelor's and master's degrees in business administration, is a doctoral trained researcher, and has carried credentials as a Certified Wellness Coach, Certified Nutrition Coach, and Certified Personal Trainer, all through the National Academy of Sports Medicine, as well as an Integrative Nutrition Coach certification from the Institute for Integrative Nutrition and a Dietary Supplement Specialist designation through the Designs for Health, a trusted leader in science-backed wellness solutions. Hulbert also co-hosts a weekly podcast, "Longevity Unlocked," with Dr. Kosubevsky, translating emerging research on detoxification, hormonal health, and regenerative therapies into real-world discussion to better educate individuals about their health.
About Kyle Hulbert
