Estimate free and bioavailable testosterone using the Vermeulen equation.
Blood Markers
Hormone Profile
Free Testosterone12.29ng/dL2.0% of total
Bioavailable T298.4ng/dL
Normal Free T ranges typically fall between 5-15 ng/dL, though this depends heavily on the lab and assay method.
About this calculator
Overview
Most testosterone in the blood is bound to proteins like SHBG and albumin. Only the 'free' portion and the portion loosely bound to albumin are considered 'bioavailable'. This tool uses the Vermeulen formula to estimate these active fractions, which are often a better indicator of hormonal health than total testosterone alone.
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Pro Tips
Blood samples for testosterone are most accurate when taken in the early morning (8-10 AM).
Albumin is usually around 4.3 g/dL for healthy adults if not measured specifically.
Reference ranges for free testosterone vary significantly between labs.
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Fun Facts
"Typically only 1-3% of total testosterone is actually 'free'."
"SHBG (Sex Hormone-Binding Globulin) levels increase with age, often lowering free testosterone."
"Bioavailable testosterone includes free T plus T weakly bound to albumin."
"Low free testosterone can cause symptoms even if total testosterone is in the 'normal' range."
Formula: Based on the Vermeulen equation for competitive binding between T, SHBG, and Albumin.
