Free Androgen Index Calculator
Enter total testosterone and SHBG in nmol/L to calculate the Free Androgen Index.
Result
How to use
- Enter your values in the fields above.
- Press Calculate to see your result instantly.
- Use the Share button to copy a link to your result.
About this calculator
Most testosterone in the blood is bound to sex hormone-binding globulin (SHBG) and is not biologically active; only the small unbound fraction acts on tissue. Rather than measuring free testosterone directly — a technically difficult assay — clinicians use the Free Androgen Index as a proxy: FAI = (total testosterone ÷ SHBG) × 100, with both values in nmol/L, giving a simple ratio that tracks how much androgen is actually available.
This calculator takes total testosterone and SHBG in nmol/L and returns the FAI. Endocrinologists and gynecologists order it as part of the hormonal workup for suspected polycystic ovary syndrome (PCOS), hirsutism, or male hypogonadism, since an elevated FAI in women or a depressed FAI in men often points to an androgen imbalance even when total testosterone alone looks borderline.
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