Calculate your Free Androgen Index (FAI) from total testosterone and SHBG lab values. The FAI estimates how much testosterone is available to your tissues, independent of what is bound to SHBG. Free, instant, no login.
Both values must be in the same units — typically nmol/L from a blood panel.
You need two values from a blood test: your total testosterone (in nmol/L) and your SHBG (in nmol/L). Both are standard markers on a hormone blood panel. Enter them and the FAI calculates immediately.
If your lab reports testosterone in ng/dL instead of nmol/L, divide by 28.84 to convert (e.g. 500 ng/dL ÷ 28.84 = 17.3 nmol/L). Most New Zealand and Australian labs report in nmol/L.
Total testosterone: 20 nmol/L
SHBG: 40 nmol/L
FAI = (20 ÷ 40) × 100 = 50
Total testosterone: 22 nmol/L (appears normal)
SHBG: 80 nmol/L (elevated)
FAI = (22 ÷ 80) × 100 = 27.5 (low — suggests high SHBG binding)
Reference ranges vary between laboratories. Broadly, for adult men:
| FAI range | General interpretation |
|---|---|
| Below 30 | Low — may indicate reduced bioavailable testosterone |
| 30 – 150 | Broadly normal range for adult men |
| Above 150 | Elevated — discuss with your doctor |
These are approximate population guidelines. Your individual reference range may differ. A low FAI alongside a normal total testosterone result often indicates elevated SHBG, which is binding and inactivating a significant portion of your testosterone. This can be clinically relevant even if total testosterone appears adequate.
Always discuss your results in context with your doctor or endocrinologist — the FAI is one data point, not a standalone diagnosis.