Key takeaways
- Only ~2% of testosterone is free.
- SHBG binds most of the rest.
- Free T can be low when total T is normal.
- Test in the morning, twice.
- Lifestyle habits matter.
When men talk about testosterone, they usually mean a single number. But the testosterone in your blood exists in different forms, and the difference can matter.
The three forms of testosterone
| Form | Approx. share | Available to the body? |
|---|---|---|
| Bound to SHBG | 44–65% | No, tightly bound |
| Bound to albumin | 33–54% | Yes, loosely bound |
| Free testosterone | ~2% | Yes, fully active |
Free plus albumin-bound testosterone is called bioavailable testosterone.
Why free testosterone matters
SHBG tends to rise with age and with some health conditions, so a man's total testosterone can look normal while his free testosterone is low. Research has linked low free testosterone to symptoms such as low libido and erection changes, even in men with normal total levels.
Common signs of low testosterone
- Low sex drive
- Erection changes
- Fatigue and low energy
- Loss of muscle, more body fat
- Low mood or poor concentration
How testing works
- Morning blood test (levels peak in the morning)
- Repeat on a second day to confirm
- Your doctor may also check SHBG, free testosterone, LH and other hormones
The American Urological Association uses a total testosterone below 300 ng/dL, together with symptoms, as a guide for diagnosing low testosterone. Reference ranges vary by laboratory.
Habits that support healthy testosterone
- Sleep 7–9 hours
- Strength train and stay active
- Maintain a healthy weight
- Limit alcohol
- Manage stress
- Get enough vitamin D, zinc and magnesium from food
Some nutrients, such as boron and tongkat ali, have been studied for their role in healthy testosterone levels and are discussed in ErecSurge's research references.
Sources
- Mulhall JP, et al. "Evaluation and management of testosterone deficiency: AUA guideline." Journal of Urology, 2018.
- Travison TG, et al. "Harmonized reference ranges for circulating testosterone levels in men." Journal of Clinical Endocrinology & Metabolism, 2017.
- Antonio L, et al. "Low free testosterone is associated with hypogonadal signs and symptoms in men with normal total testosterone." Journal of Clinical Endocrinology & Metabolism, 2016.
Common questions
What is free testosterone?
The roughly 2% of testosterone not bound to proteins, fully available to the body.
Can free testosterone be low if total is normal?
Yes, especially when SHBG is high, which often happens with age.
How is testosterone tested?
With a morning blood test, repeated on a second day.