Free Androgen Index (FAI)
Free Androgen Index (FAI) = 100 x (total testosterone / SHBG), both in nmol/L (US total testosterone ng/dL / 28.84 = nmol/L).
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Sex
- Female
- Total testosterone
- 2.5 nmol/L
- SHBG
- 30 nmol/L
Result: FAI 8.3 — above the typical female upper limit (~5), supporting androgen excess.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Women
- ~<= 5 normal; > 5 supports androgen excess (PCOS, hirsutism).
- Men
- ~30-150 typical. Unreliable at SHBG extremes; not a stand-alone free-testosterone measure in men.
What you enter
- Sex (interpretation is sex-specific)
- Total testosterone (nmol/L)
- SHBG (nmol/L)
How this is calculated
- Formula
- FAI = 100 x (total testosterone / SHBG), both in nmol/L (US total testosterone ng/dL / 28.84 = nmol/L). Unitless.
Wilke TJ, Utley DJ. Total testosterone, free-androgen index, calculated free testosterone, and free testosterone by analog RIA compared in hirsute women. Clin Chem. 1987;33(8):1372-1375. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.