Vermeulen equation with NHANES percentile ranking. The gold standard for calculating free and bioavailable testosterone from standard lab values.
Your Lab Values
From morning fasting blood draw
Sex Hormone Binding Globulin
Usually 3.5-5.5. Default 4.3 if unknown.
Demographics
Important: This calculator uses the Vermeulen equation, a validated method for estimating free testosterone. Testosterone fluctuates significantly throughout the day (highest in morning, lowest in evening) and is affected by sleep, stress, illness, and medications. A single lab draw does not define your hormonal status. Under 10 ng/dL free T should be considered clearly suboptimal for most age groups. Always work with a qualified provider to interpret results in clinical context.