Hormone Receptor Calculator
The Hormone Receptor Calculator is a scientifically accurate, free online tool that estimates the amount of biologically active (free + albumin-bound) hormones versus receptor-inactive (SHBG-bound) hormones in your bloodstream. Understanding the balance between total, free, and bound hormones is essential for diagnosing hormonal imbalances, monitoring hormone replacement therapy (HRT), and optimizing health.
About the Hormone Receptor Calculator
Hormone receptors are specialized proteins located on the surface or inside cells that bind specific hormones, triggering physiological responses. Only free hormones and those weakly bound to albumin are considered bioavailable and capable of binding to Hormone Receptor sites. Hormones tightly bound to Sex Hormone Binding Globulin (SHBG) are biologically inactive because they cannot easily dissociate and enter cells.
This Hormone Receptor Calculator uses the Vermeulen equation (published in the Journal of Clinical Endocrinology & Metabolism) — the gold-standard, peer-reviewed method — to calculate:
- Free Testosterone
- Bioavailable Testosterone (free + albumin-bound)
- Free Estradiol
- Bioavailable Estradiol
- Percentage of hormone bound to SHBG, albumin, and free fraction
Why Hormone Receptor Activity Matters
Measuring only total hormone levels can be misleading. A person may have “normal” total testosterone or estradiol, yet suffer symptoms of deficiency or excess because most of their hormone is tightly bound to SHBG and unavailable to receptors.
Elevated SHBG (common in liver disease, hyperthyroidism, pregnancy, or use of oral estrogens) reduces bioavailable hormones. Low SHBG (seen in obesity, hypothyroidism, or androgen excess) increases free fractions and receptor stimulation.
When Should You Use This Hormone Receptor Calculator?
Use this tool when you have laboratory results containing:
- Total Testosterone (ng/dL or nmol/L)
- Sex Hormone Binding Globulin – SHBG (nmol/L)
- Albumin (g/dL or g/L)
- Total Estradiol (optional)
It is especially valuable for:
- Men on TRT (testosterone replacement therapy)
- Women on HRT or birth control pills
- Individuals with symptoms despite “normal” total hormone levels
- Athletes monitoring anabolic effects
- Patients with thyroid, liver, or metabolic disorders affecting SHBG
Scientific Foundation & Accuracy
The calculations are based on the Vermeulen equation (JCEM, 1999) and Sodergard et al. (1982), which use association constants:
- Testosterone–SHBG: Ka = 1 × 10⁹ L/mol
- Testosterone–Albumin: Ka = 3.6 × 10⁴ L/mol
- Estradiol–SHBG: Ka = 0.6 × 10⁹ L/mol
These constants have been validated across thousands of clinical samples and are used by major laboratories and endocrine societies worldwide.
How to Use the Hormone Receptor Calculator
- Enter your Total Testosterone and SHBG values (mandatory)
- Enter your Albumin (default 4.3 g/dL if unknown)
- Optionally enter Total Estradiol for estradiol calculations
- Choose correct units
- Click “Calculate”
Interpretation of Results
Healthy reference ranges (approximate):
- Free Testosterone (men): 50–210 pg/mL | (women): 1–9 pg/mL
- Bioavailable Testosterone (men): 110–575 ng/dL | (women): 2–40 ng/dL
- SHBG (men): 10–57 nmol/L | (women): 18–144 nmol/L
Always discuss results with your physician. This calculator is educational and not a substitute for professional medical advice.
Disclaimer & Medical Advice
This Hormone Receptor Calculator is for informational purposes only and is not intended to diagnose or treat any medical condition. Laboratory reference ranges vary. Consult an endocrinologist or qualified healthcare provider for personalized interpretation.
Tool developed with scientific rigor and hosted with gratitude by Agri Care Hub.
