Free Testosterone Calculator

How to Use the Free Testosterone Calculator

Start by locating your total testosterone, SHBG and albumin values on your laboratory report. Enter the numbers exactly as reported and select the correct testosterone and albumin units before calculating the result.

1. Enter your serum albumin result or retain the default value where no measured albumin result is available.
2. Enter your SHBG result in nmol/L.
3. Enter your total testosterone result and choose the unit used by your laboratory.
4. Select Calculate Free Testosterone to view the estimated free and bioavailable testosterone values.

Where your testosterone result uses a different unit, use the testosterone unit conversion tool or select the relevant unit directly within this calculator.

What Is Free Testosterone?

Free testosterone is the small proportion of testosterone in the bloodstream that is not bound to a transport protein. It is considered biologically available because it can move into tissues and interact with androgen receptors.

Most circulating testosterone is attached to sex hormone-binding globulin or albumin. Testosterone bound tightly to SHBG is generally less available to tissues, while albumin-bound testosterone is more loosely attached and contributes to what is often described as bioavailable testosterone.

Total Testosterone vs Free Testosterone

Total testosterone measures all testosterone circulating in the bloodstream, including testosterone bound to SHBG, testosterone associated with albumin and the small unbound fraction.

Calculated free testosterone estimates only the unbound fraction. This distinction matters because binding-protein levels vary between individuals. Two men can have similar total testosterone results but noticeably different calculated free testosterone values.

How SHBG Affects Free Testosterone

Sex hormone-binding globulin is a protein that binds strongly to testosterone. Higher SHBG can reduce the proportion of circulating testosterone that remains free, while lower SHBG can produce a higher calculated free testosterone result relative to the same total testosterone concentration.

SHBG can be influenced by age, thyroid function, liver health, body composition, insulin resistance, medication and other physiological or medical factors.

What Does Albumin Have to Do With Testosterone?

Albumin is a protein produced by the liver that transports hormones, medicines and other substances through the bloodstream. A proportion of testosterone is loosely associated with albumin.

Can Total Testosterone Be Normal While Free Testosterone Is Low?

Yes. This can occur where SHBG is elevated and a larger proportion of circulating testosterone is tightly bound. Total testosterone may remain within the laboratory range while the estimated free fraction is comparatively low.

What Can a Low Free Testosterone Result Mean?

A lower calculated free testosterone value may be seen alongside symptoms such as reduced libido, persistent fatigue, poorer concentration, low motivation, reduced strength, slower recovery or changes in body composition.

These symptoms are not specific to testosterone deficiency. Sleep deprivation, psychological stress, thyroid disorders, calorie restriction, medication, obesity, chronic illness and other factors can produce similar complaints.

How Is Calculated Free Testosterone Estimated?

This free testosterone calculator estimates free and bioavailable testosterone using total testosterone, SHBG and albumin. The calculation is based on the binding relationships between testosterone and these circulating proteins.

How Accurate Is a Free Testosterone Calculator?

A calculated result is an estimate rather than a direct laboratory measurement. Its accuracy depends on the quality and timing of the original blood test, the entered values and the assumptions used by the calculation method.

What Blood Tests Do You Need to Calculate Free Testosterone?

At minimum, the calculation requires total testosterone and SHBG. Albumin is also used, either as a measured result or an assumed reference value.

A proper testosterone assessment may examine additional markers, including luteinising hormone, follicle-stimulating hormone, oestradiol, prolactin, thyroid function, full blood count, liver markers, kidney function and metabolic health.

Hormone blood tests should normally be collected at an appropriate time and interpreted in context. Explore the blood-testing pathway to see the screening and comprehensive testing options used during assessment.

Can a Free Testosterone Calculator Tell Me Whether I Need TRT?

No. A calculator cannot diagnose testosterone deficiency or decide whether testosterone replacement therapy is appropriate.

A responsible assessment considers symptoms, repeated hormone results, medical history, fertility plans, current medication, possible alternative causes and wider health markers.

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