Free testosterone calculator
Total T tells half the story. Enter your total testosterone, SHBG, and albumin to estimate the free and bioavailable fractions — the part that actually acts.
Why free testosterone, not just total
Most testosterone in your blood is bound to SHBG and albumin and is biologically inert. Only the small free fraction — and the loosely albumin-bound “bioavailable” portion — reaches tissue. When SHBG runs low, total T can look unremarkable while free T is high; when SHBG runs high, the reverse. That’s why two people with identical total testosterone can feel completely different.
FAQ
From total testosterone, SHBG, and albumin using the Vermeulen (1999) equilibrium equation. Only the unbound fraction is biologically active; this estimates it without a direct free-T assay.
SHBG binds most circulating testosterone. When SHBG is low — common on androgens — a larger share is free, so free T can be high even when total T looks ordinary.
It's a well-validated estimate but differs from equilibrium-dialysis free T and varies by assay. Use it for tracking trends, not diagnosis.
See free T in your full panel
FullPanel reads SHBG, free T, and 60+ markers together — in context.
Analyze free →Educational tool, not medical advice. Calculated free testosterone is an estimate and not a diagnosis.