Steroid Binding Calculator
Predict Relative Binding Affinity (RBA %) of any steroid or analog to nuclear hormone receptors using validated structure-activity relationship (SAR) models from peer-reviewed literature.
About the Steroid Binding Calculator
The Steroid Binding Calculator is a scientifically accurate, free online tool that predicts the relative binding affinity (RBA %) of natural and synthetic steroids to the five major nuclear steroid hormone receptors: androgen (AR), estrogen (ER), progesterone (PR), glucocorticoid (GR), and mineralocorticoid (MR). Built entirely on decades of peer-reviewed structure-activity relationship (SAR) studies and competitive binding assays, this calculator helps researchers, pharmacologists, and students understand receptor selectivity and potency before synthesis or testing.
Scientific Basis & Validated Formulas
Binding affinity is calculated using established SAR rules derived from thousands of compounds tested in competitive radioligand binding assays (e.g., using ³H-labeled reference ligands). Key references include:
- Raynaud et al. (1980–2000) – Comprehensive RBA tables
- Ojasoo & Raynaud (1999) – Steroid–receptor interaction maps
- Fundamental principles outlined in Steroid Binding (LibreTexts Biochemistry)
Why Steroid Binding Prediction Is Critical
Small structural changes dramatically alter receptor affinity and biological activity. For example, adding a 17α-ethynyl group converts testosterone into a progestin/estrogen, while removing the 19-methyl group (19-nor) increases progestogenic potency. Accurate prediction saves enormous time and cost in drug discovery, doping analysis, endocrinology research, and veterinary science.
When and Why You Should Use This Tool
Use the Steroid Binding Calculator whenever designing or evaluating:
- New anabolic-androgenic steroids (AAS)
- Selective androgen receptor modulators (SARMs)
- Progestins for contraception or HRT
- Anti-estrogens or aromatase-resistant compounds
- Glucocorticoids with reduced side effects
User Guidelines for Accurate Results
- Select the closest parent steroid structure.
- Apply modifications one at a time — cumulative effects are modeled.
- RBA is expressed relative to the natural ligand (e.g., Testosterone = 100 for AR; Estradiol = 100 for ER).
- Values >200 indicate super-agonists; <10 indicate very weak binding.
Interpretation of Results
RBA ≥ 100: Equal or higher affinity than natural ligand
RBA 30–99: Moderate to strong binding
RBA < 30: Weak or negligible binding
Real-World Applications
This exact methodology has been used to design modern pharmaceuticals such as drospirenone (Yasmin®), norethisterone, levonorgestrel, and many veterinary growth promoters. Sports anti-doping laboratories also rely on predicted RBAs to flag designer steroids.
For the latest in agricultural and veterinary steroid applications, visit Agri Care Hub.
Latest Advances in Steroid SAR Modeling (2023–2025)
Recent machine learning models (DeepChem, AlphaFold-based docking) have achieved >90% correlation with experimental RBA values, but transparent rule-based calculators like this one remain the gold standard for education, rapid screening, and regulatory compliance.
Common Misconceptions
Many believe anabolic rating equals binding affinity — this is false. Tissue-specific metabolism, plasma binding, and receptor co-activator recruitment also matter. This calculator focuses purely on the crucial first step: receptor binding.
The Steroid Binding Calculator delivers trustworthy, reproducible results grounded in decades of experimental data — completely free for the global scientific community.
