Free testosterone measures the small fraction of testosterone that isn't bound to carrier proteins and is therefore biologically available to interact with cells. Typically only 1-3% of total testosterone is free at any given time.
Free testosterone is often more clinically relevant than total testosterone because it's what your tissues actually use. A person can have normal total testosterone but low free testosterone if SHBG is elevated, a common pattern in aging, liver dysfunction, and thyroid imbalance. Symptoms of low testosterone (fatigue, low libido, loss of muscle) correlate more tightly with free levels than total. Sex-stratified optimal ranges apply: men's free testosterone runs substantially higher than women's, and interpretation depends on which ranges apply.
Optimal Testosterone Free: 100-200 pg/mL.
Typically re-tested every 10 weeks.
The sections below cover what the marker measures, what typical and optimal ranges look like, and what high and low results may reflect.
Free testosterone is the portion of circulating testosterone that is not attached to sex hormone binding globulin (SHBG) or albumin, which leaves it able to diffuse into tissue and bind androgen receptors.
Most testosterone in the bloodstream is not working at any given moment. A large share is bound tightly to SHBG and is effectively held in reserve. Another large share is bound loosely to albumin and can dissociate fairly easily. Only a small percentage circulates completely unbound. Clinicians often group the loosely bound and unbound portions together and call that bioavailable testosterone, while free testosterone refers to the unbound fraction alone.
That distinction matters because total testosterone measures everything at once. If SHBG is high, more of the total is locked up and the free fraction falls even when the total number looks ordinary. If SHBG is low, the opposite happens and free testosterone can sit higher than the total would suggest.
Labs estimate the free fraction in different ways. Equilibrium dialysis and ultrafiltration are the reference methods and physically separate the unbound hormone before measuring it. Calculated free testosterone is derived from total testosterone, SHBG and albumin using a published equation. Direct analogue immunoassays are cheaper but are generally considered less reliable, particularly at the low concentrations seen in women. Results usually appear in pg/mL, and some labs report ng/dL instead, where 1 ng/dL equals 10 pg/mL. Because methods differ, numbers from two labs are not always directly comparable.
It matters because the unbound fraction is the part that reaches tissue, so it tracks androgen signalling more closely than the total does in people whose binding proteins are unusual.
Androgen receptors sit in muscle, bone, brain, bone marrow, skin and reproductive tissue. Androgen signalling is involved in maintaining lean mass and strength, bone mineral density, red blood cell production, libido and aspects of mood and motivation. In women, androgens are produced in smaller amounts by the ovaries and adrenal glands and serve as precursors for oestrogen as well as acting in their own right, so both excess and deficiency can show up in skin, hair and cycle patterns.
Ageing complicates the picture. Research on androgens in the ageing male describes a gradual decline in testosterone alongside a rise in SHBG with advancing age, which means the free fraction can fall faster than the total[1]. A total result sitting comfortably inside a reference range can therefore sit next to a free result that is drifting down.
Androgen status also travels with general health rather than existing in isolation. In men with ankylosing spondylitis, research has examined the relationship between erectile dysfunction, testosterone levels and inflammatory disease activity, which illustrates how chronic inflammatory illness and sexual function tend to be studied together with androgen measures[2]. None of this makes free testosterone a standalone health score. It is one input, and it is most informative when tracked over time against symptoms and the rest of a hormone panel.
FitScript's reference range for free testosterone is 64 to 300 pg/mL for men and 0.2 to 8 pg/mL for women. FitScript uses a narrower optimal band inside that.
| Measure | Standard range | FitScript optimal range |
|---|---|---|
| Free testosterone, men | 64 to 300 pg/mL | 100 to 200 pg/mL |
| Free testosterone, women | 0.2 to 8 pg/mL | 0.5 to 4.5 pg/mL |
Published reference data for free testosterone is limited. One study of men aged 20 to 39 reported a lower cut-off, and one study of premenopausal women reported a range.[13][14]
| Sex | Age | Reference range (as shown) |
|---|---|---|
| Men | 20 to 39 | Lower cut-off 0.22 nmol/L |
| Women | 18 to 55 | 0.5 to 2.6 pg/mL |
Free testosterone results depend heavily on the method, calculated or measured, and on the assay, so these numbers are not interchangeable. Your own lab's printed range is the one to read your result against.
Reference ranges vary by laboratory, assay method, age and sex, so always read your result against the range printed on your own report. FitScript's optimal ranges are optimization targets used to guide tracking and conversation, not diagnostic cut-offs, and a value outside them is not a diagnosis of anything.
People often look for a pg/mL by age table. Free testosterone does tend to drift down with age while SHBG tends to rise[1], but published age bands differ so much between assays and populations that a single table would be misleading. The more useful comparison is your own result against your own previous results, drawn at the same time of day and ideally by the same method.
A high result means more unbound androgen is available to tissue than expected, which may reflect genuine androgen excess, a low SHBG shifting the balance, or an outside source of testosterone.
People with elevated free androgens often report acne, oily skin, coarse hair growth on the face, chest or abdomen, thinning hair at the scalp, irregular or absent menstrual cycles, and changes in mood or sleep. In men, a high free result frequently reflects exogenous testosterone or anabolic steroid use rather than natural overproduction, and may come with acne, irritability and a rising haematocrit on a blood count.
Common contributors include polycystic ovary syndrome, which is the most frequent cause of androgen excess in women of reproductive age. Professional guidance on screening and managing the hyperandrogenic adolescent sets out how clinicians approach new hirsutism, acne and cycle irregularity in younger patients[3], and the summary version of that guidance covers the same assessment pathway[4]. Low SHBG, which is associated with insulin resistance and excess body fat, raises the free fraction without necessarily raising the total. Adrenal causes such as nonclassic congenital adrenal hyperplasia and, far more rarely, androgen-secreting tumours are also considered. Rapidly progressive virilization is worth discussing with a clinician promptly rather than monitoring at home.
Over the longer term, the concern with sustained androgen excess in women is usually its metabolic company, since insulin resistance and adverse lipid patterns often travel alongside it, plus the effects on cycles and fertility. With exogenous androgen use, the issues clinicians watch include suppression of natural production, red cell changes and fertility. A high value is a reason to investigate, not a diagnosis on its own.
A low result means less unbound androgen is reaching tissue, which may reflect reduced production, a high SHBG binding more of the total, or a temporary suppression from illness, stress or energy deficit.
Reported symptoms in men include low libido, erectile difficulty, persistent fatigue, loss of strength and lean mass despite training, low mood, irritability, poor sleep and slower recovery between sessions. In women, low androgen levels are sometimes discussed alongside reduced libido and low energy, though the link is not settled and no single threshold defines deficiency.
Contributors are varied. Age-related decline with a parallel rise in SHBG is well described[1]. Excess body fat and insulin resistance are associated with lower testosterone in men. Chronic inflammatory disease is another recognised context in which testosterone and sexual function are studied together[2]. Pituitary causes are also assessed, including raised prolactin, which research has linked with changes in insulin sensitivity as well as with disrupted gonadal signalling[5]. Poor sleep, heavy alcohol intake, prolonged low energy availability and very high training loads without recovery are all associated with lower readings.
Long term, consistently suboptimal androgen signalling is associated with reduced bone mineral density, less favourable body composition and poorer metabolic markers, although association is not the same as cause. The sensible sequence is observation, then context, then conversation. A single low number taken in the afternoon after a bad week of sleep means little. A pattern of low results on morning draws, alongside symptoms, is worth discussing with a clinician who can assess the whole picture, including total testosterone, SHBG, LH, FSH and prolactin.
More than most people expect, which is why timing and consistency matter as much as the number itself.
Testosterone follows a daily rhythm and is generally highest in the morning, so most clinicians prefer an early draw and a repeat before drawing conclusions. Acute illness, a night of broken sleep, a very hard training session the day before, significant weight change and recent surgery can all shift results. High-dose biotin supplements can interfere with some immunoassays. Assay method matters too, since a calculated free testosterone and an equilibrium dialysis result are not interchangeable.
Medications are a frequent and underappreciated influence. A review of cardiovascular and pulmonary medications and male reproduction describes how several widely used drug classes can affect reproductive hormones and function[6]. Insulin-sensitising medicines have been examined in polycystic ovary syndrome, where work on metformin and glitazones looked at their effects in that population[7]. A licensed provider evaluates whether any prescription treatment is appropriate, and no medication should be started or stopped based on a web page.
Diet, training and supplements have been studied mostly in specific populations. Myo-inositol with folic acid has been assessed in women with polycystic ovary syndrome[8], and a systematic review examined the impact of ketogenic diets on weight, metabolic and endocrine parameters in the same group[9]. A randomised controlled trial of combined resistance and endurance training in women with polycystic ovary syndrome reported changes across hormonal, metabolic, inflammatory and oxidative stress biomarkers[10]. On the supplement side, purified shilajit has been evaluated for its effect on testosterone levels in healthy volunteers[11], and a 12-week randomised controlled trial examined whether creatine causes hair loss, a question that comes from its presumed link to androgen metabolism[12]. These findings are suggestive rather than settled, and results in one population do not automatically transfer to another.
Free testosterone is measured as part of a hormone panel, always alongside total testosterone and SHBG, because the three only make sense together.
FitScript is a labs-first membership built on repeat testing rather than a single snapshot, with 150+ biomarkers tested per year so that androgen markers can be followed across seasons, training blocks and body composition changes. Draws are scheduled for consistency, which is what makes one result comparable to the next.
Atlas, FitScript's AI health advisor, reads the result in context rather than in isolation, comparing it against the typical lab range, the optimal range, previous draws and related markers, then writing that interpretation into your FitScript. Where a result sits outside the optimal band, the output describes what the pattern may reflect and what is worth raising, not what condition you have. Where a prescription option such as testosterone therapy comes up, a licensed provider reviews your labs, history and symptoms and decides whether it is appropriate. Treatment choice, formulation and monitoring are clinical decisions and are never set by an article or an algorithm.
This page is educational and is not medical advice. Discuss your results and any treatment with a clinician or licensed provider who can see your full history.
Free testosterone is close to uninterpretable alone, so it is read with the markers that produce it, bind it, convert it and suppress it.
Start with Testosterone Total, which gives the full circulating pool, and SHBG, the binding protein that largely decides how much of that pool stays free. DHEA-S reflects adrenal androgen output and helps separate ovarian from adrenal patterns of androgen excess. Estradiol matters because testosterone is aromatised into oestrogen, and the balance between them affects symptoms in both sexes. IGF-1 sits alongside as a growth and anabolic signal that responds to training, sleep and nutrition. Cortisol is worth seeing too, since sustained stress and disrupted sleep are associated with suppressed gonadal signalling. These are typically drawn together on hormone lab panels, the Hormone Panel for him and the Hormone Panel for her rather than ordered one at a time.
Free testosterone is the unbound, tissue-available fraction of your total testosterone, and it is shaped as much by SHBG as by how much hormone you make. FitScript's reference range for men is 64 to 300 pg/mL, with its optimal band at 100 to 200 pg/mL and 0.5 to 4.5 pg/mL for women. High and low results each have several plausible explanations, most of them modifiable or at least investigable. Test in the morning, repeat before concluding, and read the number next to total testosterone, SHBG and your actual symptoms.
Calculators that use Testosterone Free:
FitScript's reference range for free testosterone is 64 to 300 pg/mL for men and 0.2 to 8 pg/mL for women. FitScript's optimal range is 100-200 pg/mL for men and 0.5-4.5 pg/mL for women, which are optimization targets rather than diagnostic cut-offs. Always compare your result against the range printed on your own lab report, since ranges vary by lab, method, age and sex.
Women carry far less free testosterone than men, and FitScript's optimal range for women is 0.5-4.5 pg/mL. Standard lab reference ranges for women differ widely depending on the assay used, and direct immunoassays are generally considered less reliable at these low concentrations. Because of that variability, a result is most useful read against the same lab's range, alongside total testosterone, SHBG and DHEA-S, and interpreted with a clinician.
Usually because SHBG is high. Sex hormone binding globulin binds testosterone tightly and holds it out of circulation, so a high SHBG can leave the total looking unremarkable while the unbound, tissue-available fraction falls. SHBG tends to rise with age. Thyroid status, liver health, oestrogen levels and some medications also influence SHBG.
Testosterone follows a daily rhythm and is generally highest in the morning, so an early draw gives the most comparable result. Repeat testing matters more than a single value, since acute illness, broken sleep, a very hard training session the day before, significant weight change and recent surgery can all shift a reading. Keeping the time of day and the testing method consistent is what makes one result comparable to the next.
Equilibrium dialysis and ultrafiltration are considered the reference methods because they physically separate the unbound hormone before measuring it. Calculated free testosterone is derived from total testosterone, SHBG and albumin using a published equation and performs reasonably well in most situations. Direct analogue immunoassays are cheaper but are generally viewed as less reliable, particularly at low concentrations. Results from different methods are not directly interchangeable.
Sleep, body composition, alcohol intake, training load and recovery are all associated with androgen levels, and changes in body fat and insulin sensitivity also shift SHBG, which changes the free fraction. Combined resistance and endurance training and ketogenic diets may shift hormonal and metabolic markers in women with polycystic ovary syndrome. Findings are suggestive rather than settled, and results in one population do not automatically apply to another.
No. A single value cannot diagnose any condition. Polycystic ovary syndrome is the most common cause of androgen excess in women of reproductive age, but low SHBG, adrenal conditions, exogenous androgen use and, rarely, androgen-secreting tumours are also considered. Professional guidance sets out how clinicians assess new hirsutism, acne and cycle irregularity. Rapidly progressive virilization is worth discussing with a clinician promptly.
Not on its own. A low reading taken at the wrong time of day, during illness or after a period of poor sleep may not reflect your usual level, which is why repeat morning testing is standard. If a pattern of suboptimal results appears alongside symptoms, a licensed provider evaluates the full picture, including total testosterone, SHBG, LH, FSH and prolactin, and decides whether any prescription treatment is appropriate.