What is Free Testosterone?
Free testosterone is the roughly 1–2% of total testosterone that circulates unbound to proteins and can enter cells to exert its effects. Because most testosterone is tightly bound to SHBG, free testosterone can better reflect true androgen status than total testosterone especially when SHBG is abnormal.
Why it matters
Two people with identical total testosterone can have very different free testosterone if their SHBG differs. Free testosterone helps explain symptoms of low or high androgen activity when total levels look normal.
What it measures
The concentration of testosterone not bound to SHBG or albumin, measured directly (equilibrium dialysis is the reference method) or calculated from total testosterone, SHBG, and albumin.
Reference & optimal ranges
Reference ranges vary by lab, assay, age, and sex. The ranges below reflect commonly published adult intervals and are for education only always interpret results with the range printed on your own lab report and a clinician.
Elevated free testosterone can occur with low SHBG (insulin resistance, obesity) or androgen excess such as PCOS in women.
Common symptoms
- Acne, oily skin
- In women: hirsutism, irregular cycles
- Male-pattern hair changes
Potential causes
- Low SHBG from insulin resistance
- PCOS
- Exogenous testosterone or steroids
Low free testosterone with normal total testosterone often reflects high SHBG, common with aging, hyperthyroidism, or liver disease.
Common symptoms
- Low libido
- Fatigue
- Reduced muscle mass
- Low mood
Potential causes
- High SHBG
- Hypogonadism
- Aging
- Chronic illness
How to improve your Free Testosterone
Lifestyle
Improve insulin sensitivity
Reducing insulin resistance normalizes SHBG, which shifts the free fraction.
Nutrition
Balanced macronutrients
Support healthy SHBG and total testosterone as covered on the testosterone page.
Exercise
Resistance training
Improves body composition and androgen sensitivity.
Sleep
Consistent sleep
Supports overall testosterone production.
Frequently asked questions
Scientific references
- Free & Bioavailable Testosterone Calculator and background International Society for the Study of the Aging Male (ISSAM)
- Testosterone Levels Test MedlinePlus, U.S. National Library of Medicine
Educational information, not medical advice. This page is for general education and does not replace diagnosis or treatment by a licensed clinician. Do not start, stop, or change any medication, supplement, or treatment based on this content. Reference and optimal ranges vary between laboratories interpret your results with the range on your own report and a qualified professional.