How do you calculate the Free Androgen Index?

FAI = (total testosterone divided by SHBG) x 100, with both values in nmol/L. For example, a testosterone of 1.6 nmol/L and SHBG of 45 nmol/L gives an FAI of about 3.6.

Does a high FAI mean I have PCOS?

No. FAI is only one of several things a clinician looks at, and it cannot diagnose any condition on its own. A raised FAI can have several causes. If your value concerns you, or you have symptoms, speak to your GP.

Why is my FAI high when my testosterone is normal?

FAI reflects how much testosterone is not bound to SHBG. If your SHBG is low, more testosterone is unbound, so the FAI rises even when the total reads normal. The reverse happens when SHBG is high.

Helvy tool · Free

Free Androgen Index Calculator

The Free Androgen Index compares your total testosterone to your SHBG. Enter both in nmol/L to see your FAI and where it sits against commonly quoted bands.

Total testosterone (nmol/L)

SHBG (nmol/L)

How this is worked out

FAI is calculated as (total testosterone ÷ SHBG) × 100, with both values in nmol/L, the standard formula printed by UK laboratories. Reference bands vary between labs: an FAI up to about 5 is a range commonly quoted for premenopausal women, and roughly 24 to 104 for adult men. Always read the range on your own report, and note that FAI falls naturally after menopause. This is reference context only, not a diagnosis.

This tool is for general wellbeing information and is not a diagnosis or medical advice. It places the numbers you enter in context; it cannot tell you whether you have a condition. If a result concerns you, or you have symptoms, speak to your GP.

Questions

How do you calculate the Free Androgen Index?: FAI = (total testosterone divided by SHBG) x 100, with both values in nmol/L. For example, a testosterone of 1.6 nmol/L and SHBG of 45 nmol/L gives an FAI of about 3.6.
What is a normal Free Androgen Index?: Reference bands vary between laboratories. An FAI up to about 5 is a range many UK labs quote for premenopausal women, and roughly 24 to 104 for adult men. The range printed on your own report is the one that counts, and FAI falls naturally after menopause.
Does a high FAI mean I have PCOS?: No. FAI is only one of several things a clinician looks at, and it cannot diagnose any condition on its own. A raised FAI can have several causes. If your value concerns you, or you have symptoms, speak to your GP.
Why is my FAI high when my testosterone is normal?: FAI reflects how much testosterone is not bound to SHBG. If your SHBG is low, more testosterone is unbound, so the FAI rises even when the total reads normal. The reverse happens when SHBG is high.

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Hormone Balance

5 markers

Female hormone balance — FSH, LH, SHBG, testosterone, and free androgen index.

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Helvy

Helvy tool · Free

Free Androgen Index Calculator

The Free Androgen Index compares your total testosterone to your SHBG. Enter both in nmol/L to see your FAI and where it sits against commonly quoted bands.

Total testosterone (nmol/L)

SHBG (nmol/L)

How this is worked out

Questions

How do you calculate the Free Androgen Index?: FAI = (total testosterone divided by SHBG) x 100, with both values in nmol/L. For example, a testosterone of 1.6 nmol/L and SHBG of 45 nmol/L gives an FAI of about 3.6.
What is a normal Free Androgen Index?: Reference bands vary between laboratories. An FAI up to about 5 is a range many UK labs quote for premenopausal women, and roughly 24 to 104 for adult men. The range printed on your own report is the one that counts, and FAI falls naturally after menopause.
Does a high FAI mean I have PCOS?: No. FAI is only one of several things a clinician looks at, and it cannot diagnose any condition on its own. A raised FAI can have several causes. If your value concerns you, or you have symptoms, speak to your GP.
Why is my FAI high when my testosterone is normal?: FAI reflects how much testosterone is not bound to SHBG. If your SHBG is low, more testosterone is unbound, so the FAI rises even when the total reads normal. The reverse happens when SHBG is high.

Test for this

The panel that covers this

Hormone Balance

5 markers

Female hormone balance — FSH, LH, SHBG, testosterone, and free androgen index.

from £99View panel

Compare all panels Not sure? Find my test

Free Androgen Index Calculator

The panel that covers this

Hormone Balance

A clearer picture of your health starts with a single drop.

Free Androgen Index Calculator

The panel that covers this

Hormone Balance

A clearer picture of your health starts with a single drop.