Free Androgen Index (FAI) Calculator

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Total testosterone (nmol/L)

SHBG (nmol/L)

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How this is worked out. FAI = (total testosterone nmol/L / SHBG nmol/L) × 100. Both inputs must be in nmol/L — entering testosterone in ng/dL is the single commonest way this one is got wrong.

Men: roughly 35–92% is typical. Women: >5% suggests androgen excess (a supporting marker in PCOS). Note the input is nmol/L — use the converter tab if your result is in ng/dL (divide by 28.84).

The bands on this page

Result	What it is called here
under 15	Low androgen availability
15 to 30	Mid-range
30 to 95	Upper range
over 95	High

What goes in, and where each number comes from

Every input is a real test. Follow one to see its normal range, its optimal range and what moves it — the calculation is only as good as the numbers you feed it.

Total Testosterone →$49.50

SHBG (Sex Hormone-Binding Globulin) →$22.50

What it costs to actually get these numbers

The 2 tests on their own	$72.00
The cheapest panel that covers them — Male Hair Loss — What Blood Can and Cannot Tell You (10 markers)	$160.65

Order the tests, not the panel. This calculation needs 2 results, and buying them individually is $88.65 cheaper than the smallest panel that happens to contain them. The panel is worth it only if you want the other 8 markers on it too.

Order Male Hair Loss — What Blood Can and Cannot Tell You →

Prices are Marek Diagnostics with the 10% code already applied, and they are what was filed when this page was built — check the cart. Ordering through these links pays a commission at no cost to you.

What could have moved the measurement, not the marker

A wrong number and a real change look identical on a report. These are the reasons a result here can be an artifact of how the blood was drawn or run, and they are worth ruling out before anything else.

assayImmunoassay vs LC/MS

Direct immunoassays are unreliable at the low end and in women. LC-MS/MS is the reference method.

What to do: Ask for LC/MS where the number will drive a decision.

timingTime of day

Testosterone peaks in the early morning and falls through the day, with the difference largest in younger men — a 4pm draw can read 20–30% below the same man at 8am.

What to do: Draw before 10am, and always at the same time when tracking.

timingFasting state

Rises after eating, so a non-fasted draw measures your breakfast rather than your baseline.

What to do: Draw fasted, 10–12 hours, water only.

timingRoute and timing of any estrogen

Oral estrogen raises SHBG two- to fourfold through first-pass liver metabolism; transdermal barely touches it. So the same hormone at the same dose produces completely different SHBG depending only on how it was taken.

What to do: Record the route, not just the hormone — an SHBG drawn on oral estrogen cannot be compared to one drawn off it.

5 more interferences are listed on the marker pages themselves: Total Testosterone · SHBG (Sex Hormone-Binding Globulin).

This tool does not diagnose anything. It puts a number next to a published interval and shows the arithmetic that got there. It cannot see your symptoms, your medications, your history or the assay your lab ran. A result outside the outer bounds belongs in front of a clinician, not in a supplement search.

Where to go with this

Read one of these results on its ownType a value, pick your units and sex, and see where it sits and what could have moved it.The Male Hair Loss — What Blood Can and Cannot Tell You10 markers, $160.65 with the code — what it settles and what it does not.Every marker on this site103 markers, each with the normal range, the optimal range and what moves it.

The other hormones calculations

Free Testosterone (Vermeulen)Calculates free testosterone from total T, SHBG and albumin — far more reliable than direct analog assays.Testosterone : Estradiol Ratio (men)Balances your androgen and estrogen signal. Useful when symptoms don't match either value alone.Progesterone : Estradiol Ratio (Pg/E2)The classic 'estrogen dominance' index in women — whether progesterone is adequately balancing estradiol in the luteal phase.