Pindrop

Free Testosterone Calculator

Estimate free and bioavailable testosterone from a standard lab panel using the Vermeulen equation. You need total testosterone, SHBG, and albumin.

ng/dL
nmol/L
g/dL

Optional. Defaults to 4.3.

Free testosterone

113.1pg/mL

1.89% of total · reference 50–210 pg/mL (men 20–49)
Free T
113.1pg/mL
Free %
1.89%
Bioavailable T
275ng/dL
Bioavailable %
45.83%

Vermeulen et al. (1999). Reference range for bioavailable T in men is roughly 110–575 ng/dL. For information only, not a diagnosis.

What this calculator does

Most of the testosterone in your blood is bound to proteins and not available to your tissues. Only a small free fraction, plus a loosely albumin-bound part, actually does anything. A total testosterone number alone can look normal while the free portion is low, which is why the free and bioavailable figures matter. This calculator estimates both from a routine lab panel.

It uses the Vermeulen equation, the method most endocrinology references rely on. Enter total testosterone in ng/dL or nmol/L, SHBG in nmol/L, and albumin in g/dL. Albumin is optional; if you leave it out, a standard 4.3 g/dL is assumed, which is close enough for most people.

Reading the result

Free testosterone is shown in pg/mL with its percentage of total, next to a typical adult-male reference range for context. Bioavailable testosterone, the free plus albumin-bound portion, is shown in ng/dL. These are estimates from an equation, not a direct measurement, and reference ranges vary by lab and age. Bring the numbers to your provider rather than acting on them alone.

Common questions

How do you calculate free testosterone?
The common method is the Vermeulen equation, which estimates free testosterone from your total testosterone, SHBG, and albumin. It models how tightly each protein holds testosterone and works out how much is left unbound. This calculator uses that formula, so you just enter your lab numbers.
What is the difference between free and bioavailable testosterone?
Free testosterone is the small fraction, usually 1 to 3%, floating unbound in your blood. Bioavailable testosterone is that free portion plus the loosely bound part stuck to albumin, which your body can still use. The testosterone locked onto SHBG counts as neither.
What does SHBG do to testosterone?
SHBG, or sex hormone binding globulin, grabs testosterone and holds it tightly, pulling it out of circulation. The more SHBG you have, the less free testosterone is available even when your total looks fine. That is why high SHBG can leave you with low-T symptoms despite a normal total number.
Why is my total testosterone normal but free testosterone low?
Usually high SHBG. If a lot of your testosterone is bound to SHBG, the total reads fine but the usable free portion is small. This is a common pattern, and it is the main reason a free testosterone calculation tells you more than the total alone.
What is a normal free testosterone level?
Lab ranges vary, but adult men often land somewhere around 5 to 25 ng/dL of free testosterone depending on age and the lab method. Because reference ranges differ so much by assay, compare your result to your own lab range rather than a fixed number. Symptoms matter as much as the value.
Do I need to enter albumin?
Not usually. Albumin barely moves between people, so the calculator defaults to 4.3 g/dL, a normal value. If you have a recent albumin result you can enter it for a slightly more precise number, but the default is fine for most people.

Pindrop is a calculation tool, not medical advice. Confirm your dose and protocol with a licensed healthcare provider.