Free Testosterone Calculator
Estimates free (bioavailable) testosterone. Enter total testosterone alone for a quick estimate, or add SHBG for a more accurate Vermeulen calculation. Important for BHRT/TRT patients.
Method
Vermeulen equation (when SHBG provided), or simplified estimate: Free T ≈ Total T × 0.0311
Optional — improves accuracy
Default 4.3 g/dL
When is this useful?
Only about 2–3% of testosterone circulates freely in the blood. The rest is bound to SHBG and albumin. Total testosterone can look normal while free testosterone is actually low (or vice versa).
Especially relevant for women on BHRT — Quest total testosterone is known to inflate results for women on testosterone therapy. Free testosterone gives a more accurate picture of bioavailable hormone levels.
For clinical decisions, a direct free testosterone measurement (equilibrium dialysis) is more accurate than any calculation.