With testosterone, you hear two numbers: total and free. They sound almost the same, but the difference can decide whether a result matches how you feel. Total testosterone measures everything, free testosterone only the part your body can use directly.
This article explains the difference, why SHBG sits in the middle of it, and when which value is more informative.
What is total testosterone?
Total testosterone measures all the testosterone in your blood, both the part bound to proteins and the free part. It's the most commonly measured value and often the starting point.
Most of your testosterone is bound to proteins, mainly SHBG and albumin. That bound part isn't directly available to your cells.
So total testosterone can give a distorted picture if you don't know the rest.
What is free testosterone?
Free testosterone is the small part that isn't attached to proteins and is therefore biologically active. It's this part your cells can actually use.
In most men only a few percent of the total is truly free. Yet that small part is often the most relevant to complaints.
Free testosterone is usually calculated from total testosterone and SHBG, or sometimes measured separately.
Why SHBG makes the difference
SHBG is the protein that binds testosterone. The higher your SHBG, the more testosterone is bound and the less is freely available. So two men with the same total testosterone can have very different free testosterone.
| Situation | Effect on free testosterone |
|---|---|
| High SHBG, normal total | Less free testosterone available |
| Low SHBG, normal total | More free testosterone available |
Researchers show that a calculation of free testosterone based on SHBG is often more informative than total testosterone alone (Vermeulen et al., J Clin Endocrinol Metab, 1999). What SHBG does and what makes it fluctuate is in SHBG explained.
Which value is more informative when?
For many men total testosterone gives a fine first impression. If your complaints and your total testosterone don't line up, free testosterone can add to the picture.
The NHG stresses that testosterone values are always looked at together with your symptoms, and that one measurement says little. The time of the draw also counts, because testosterone is highest on average in the morning.
A handy rule of thumb: start with total testosterone and look at free testosterone if the picture doesn't add up. That way you don't base too many conclusions on one number.
If you want total testosterone, free testosterone and SHBG measured together, a men's hormone test brings them into view. For normal values and a low value, read testosterone levels in men, and the broader frame is in the pillar men's hormones.
Frequently asked questions
Is free testosterone more important than total? Not always. They often complement each other; free testosterone is mostly useful when total and your complaints don't line up.
Can my total be normal and my free low? Yes, for example with a high SHBG. Then your free testosterone can come out lower while total looks normal.
Is free testosterone measured or calculated? Often calculated from total testosterone and SHBG, sometimes measured separately in the lab.
Why do I feel tired with a normal testosterone? Sometimes it's in your free testosterone, sometimes in very different causes like sleep or thyroid. A blood value helps separate directions.
When is the best time to measure testosterone? Testosterone is highest on average in the morning, so a morning draw gives a more representative picture.
Is a single measurement enough? Often not. One value can deviate, and a repeat gives a more reliable picture.
What you can do with this
Total and free testosterone together tell a fuller story than each alone. If your result and your complaints don't line up, free testosterone is the piece to look at. In doubt or have complaints? Discuss it with your GP.
Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss symptoms and treatment decisions with your GP.
References
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999. PMID: 10523012.
- NHG. Dutch College of General Practitioners: hormonal diagnostics. Accessed 2026.
- RIVM. Public health and care: men's health. Accessed 2026.
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