Free testosterone — the active fraction, and why total T can mislead
Paired condition: Low testosterone in men
Quick answer
Free testosterone is the fraction of your circulating testosterone that's *not* bound to proteins (mainly SHBG and albumin). It's the active form available to tissues. Most of your testosterone is bound — typically only 1–4% circulates "free." Free T correlates better with symptoms than total T does, which is why "normal total testosterone" can still pair with low free T (and symptomatic hormonal pictures) when SHBG is high.
Reference ranges and interpretation
| Value / population | Classification | What it means |
|---|---|---|
| Adult male | 5 – 21 ng/dL | Or 50 – 210 pg/mL depending on lab units. The bioavailable fraction. |
| Adult female (reproductive age) | 0.1 – 6.4 pg/mL | Typical reproductive-age range. |
| Postmenopausal female | 0.1 – 3.0 pg/mL | Lower than reproductive years. |
Methodology matters. Calculated free T (from total T + SHBG + albumin) is widely available and usually adequate. Direct equilibrium dialysis or LC-MS measurement of free T is the gold standard, often used in research settings. Some "free T" assays (older analog methods) have known reliability problems.
What different values typically indicate (men)
What different values typically indicate (women)
What to look at alongside free testosterone
- SHBG — the binding protein. Low SHBG raises free T; high SHBG lowers free T
- DHEA-S — adrenal androgen contribution
- LH + FSH — pituitary signal pattern (distinguishes primary vs secondary hypogonadism)
- Estradiol — testosterone converts to estradiol via aromatase
- Fasting insulin + HOMA-IR — insulin resistance is a major driver of low SHBG (raising free T) in women
- Prolactin — high prolactin suppresses GnRH and downstream T
Why total T can mislead — the SHBG story
- Estrogen exposure (combined oral contraceptives, transdermal estrogen)
- Hyperthyroidism
- Liver disease
- Calorie restriction / low body fat
- Obesity
- Hypothyroidism
- Polycystic ovary syndrome
- Some medications (anabolic steroids, glucocorticoids)
Phi Longevity reads every marker on every lab you upload — together, against your history, against optimal ranges, and across time. The integrated picture tells you what a single number can't.
Start with my labs →Frequently asked questions
Should I get total T or free T tested?
Both. Plus SHBG to make the interpretation reliable. The standard "men's hormone panel" should include total T + free T + SHBG at minimum.
Why does my free T vary so much between draws?
Testosterone has a diurnal rhythm — highest in the morning, lower by late afternoon. It also pulses. Consistent morning draws (8–10 AM) give the most comparable longitudinal values. Acute stress, illness, sleep deprivation, and recent intense exercise all shift T.
Are "free T" assays reliable?
Calculated free T (from total T + SHBG + albumin) is widely used and adequate for most clinical decisions. Direct equilibrium dialysis or LC-MS direct measurement is more accurate. Older analog "direct" free T assays are known to have reliability problems and should be interpreted cautiously.
Why is free T low after starting hormonal contraceptives?
Combined oral contraceptives raise SHBG and suppress ovarian androgen production. Both effects lower free T. Symptoms (libido, mood, energy) can emerge over months. The trade-off is real and worth discussing with your provider.
My free T is elevated and I'm female — is that PCOS?
It's one of the PCOS criteria, but the diagnosis requires more than a single elevated androgen. The Rotterdam criteria require two of: hyperandrogenism (clinical or biochemical), oligo-/anovulation, polycystic ovarian morphology on ultrasound — plus exclusion of other causes (thyroid, prolactin, congenital adrenal hyperplasia). See the [PCOS condition page](/lab-results/pcos).
References
All citations verified against PubMed / publisher of record 2026-05-26.
- 1.Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA. (2018). Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 103(5):1715-1744. — Standard reference for free testosterone measurement methodology: equilibrium dialysis is the gold standard; Vermeulen formula calculation is the practical alternative; older analog "direct" free-T assays have known reliability problems.PubMed →DOI →
- 2.Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group. (2004). Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome (PCOS). Human Reproduction. 19(1):41-47. — Reference for hyperandrogenism (clinical or biochemical) as a PCOS criterion; basis for the elevated-free-T-in-women interpretation framing.PubMed →DOI →
- 3.Vermeulen A, Verdonck L, Kaufman JM. (1999). A critical evaluation of simple methods for the estimation of free testosterone in serum. Journal of Clinical Endocrinology & Metabolism. 84(10):3666-3672. — The Vermeulen formula: free T = f(total T, SHBG, albumin). Widely used for calculated free T; basis for "SHBG is the missing piece" framing.PubMed →DOI →
Free T reference ranges quoted are typical US clinical laboratory ranges; specific cutoffs vary substantially by assay methodology and laboratory. Every link above opens the PubMed abstract or publisher's DOI landing page in a new tab. All citations verified vs PubMed / publisher of record 2026-05-26.
By Steve Pinedo
Co-founder, Phi Longevity
Last updated: 2026-05-26
Steve Pinedo is the Co-founder of Phi Longevity, the AI application that turns a confusing stack of lab reports, wearable data, and clinical notes into a single, integrated picture of your health. He started Phi Longevity to make proactive health and wellness far easier to achieve. He realized how difficult it was for clients to manage their own care, records and coordination so he assembled a comprehensive M.D. led clinical team behind the platform, packaging the proactive-care experience that delivered measurable outcomes (lower triglycerides, reduced body fat, improved LDL, balanced hormones, relief from long-running autoimmune conditions) for any patient with a complicated lab to use now with an application. More about Phi Longevity →