Free Testosteronenmol/L
Bioavailable testosterone
Also known as: Free Testosterone (calculated)
Typical optimal range
0.2–0.62 nmol/L
Female
A commonly cited optimal range for calculated free testosterone is approximately 0.2–0.62 nmol/L, though reference intervals differ between laboratories, calculation methods, and sex, so always interpret your result in the context of the ranges provided by your own lab. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of testosterone and androgen deficiency in clinical practice follows NICE guidance and British Society for Sexual Medicine (BSSM) guidelines, with laboratory interpretation aligned to NHS and Association for Clinical Biochemistry standards.
What is Free Testosterone?
Free testosterone is the small fraction of testosterone — roughly 1–2% of the total — that circulates unbound to carrier proteins such as sex hormone-binding globulin (SHBG) or albumin, meaning it can pass directly into cells and exert hormonal effects. It is produced mainly by the testes in men and, in smaller amounts, by the ovaries and adrenal glands in women. Because SHBG levels can vary considerably between individuals, total testosterone alone can sometimes give a misleading picture; measuring the free fraction — usually calculated from total testosterone, SHBG, and albumin — gives a more accurate reflection of how much testosterone is actually biologically available to the body's tissues.
What a high Free Testosterone means
A raised free testosterone result is a prompt to look more closely at what might be shifting the balance between bound and unbound hormone — it is not a diagnosis in itself, and context matters enormously.
- Low SHBG. SHBG is the main carrier protein for testosterone, so when SHBG falls, more testosterone circulates freely. Low SHBG is commonly seen with insulin resistance, type 2 diabetes, obesity, and non-alcoholic fatty liver disease (now termed MASLD in UK practice) — conditions your GP may want to screen for if your SHBG is unexpectedly low.
- Polycystic ovary syndrome (PCOS). In people assigned female at birth, elevated free testosterone — even when total testosterone is at the upper end of normal — is one of the recognised biochemical features of PCOS and is worth discussing with a GP, particularly alongside symptoms such as irregular periods or excess hair growth.
- Exogenous androgens or supplements. Testosterone-containing medications, anabolic steroids, or some DHEA supplements can raise free testosterone directly and should always be disclosed when blood results are reviewed.
Free testosterone results can be influenced by the time of day blood is drawn (levels peak in the morning), acute illness, and the calculation method used; a single elevated reading should be interpreted cautiously alongside symptoms and repeat testing.
What a low Free Testosterone means
A low free testosterone level is generally considered a more clinically meaningful indicator of androgen deficiency than a low total testosterone alone, because it reflects how much hormone is actually available to tissues — symptoms such as fatigue, low mood, reduced libido, or loss of muscle mass become more relevant in this context.
- Elevated SHBG. High SHBG binds more testosterone and reduces the free fraction; SHBG rises with ageing, liver disease, hyperthyroidism, and oestrogen-containing medications such as the combined oral contraceptive pill.
- Primary or secondary hypogonadism. Conditions affecting the testes, ovaries, or the pituitary-hypothalamic axis — including Klinefelter syndrome, hyperpituitarism, or significant chronic illness — can reduce testosterone production overall, which will be reflected in a low free fraction as well as low total testosterone.
In women, free testosterone naturally varies across the menstrual cycle and declines with age and around the menopause; interpretation should always account for age, sex, and stage of reproductive life.
Should I be worried?
A single out-of-range free testosterone reading rarely tells the full story on its own, and it is worth knowing that the calculated result is only an estimate — direct measurement methods also exist and may be used in specialist settings. If your result is flagged as high or low, the most useful next step is to book a GP appointment to discuss it alongside your symptoms, your total testosterone, SHBG, and any other relevant markers such as LH, FSH, or thyroid function. Mild deviations in the absence of symptoms are often not clinically significant, while a result that fits with how you are feeling is worth taking seriously. Your GP can decide whether a repeat test, a referral to endocrinology, or further investigation is appropriate — there is no need to worry, but equally no need to ignore a result that doesn't seem right.
What actually helps
Several well-supported lifestyle factors can help maintain healthy testosterone availability and SHBG balance.
- Manage insulin resistance. Improving insulin sensitivity — through a lower-refined-carbohydrate diet, regular physical activity, and weight management — is one of the most effective ways to normalise SHBG and, in turn, free testosterone; this is particularly relevant if low SHBG is driving elevated free T.
- Strength and resistance training. Regular resistance exercise is consistently associated with maintained testosterone levels and improved body composition; even two to three sessions per week has meaningful benefit according to mainstream exercise physiology evidence.
- Prioritise sleep. Testosterone secretion follows a circadian rhythm and peaks during sleep; poor or short sleep duration is associated with reduced testosterone levels in well-replicated studies, making consistent, good-quality sleep a practical lever.
- Maintain a healthy body weight. Excess adipose tissue — particularly visceral fat — raises oestrogen and lowers SHBG, reducing free testosterone availability; even modest weight loss in those with overweight or obesity can produce meaningful hormonal improvements.
Certain dietary patterns have reasonable supporting evidence for maintaining healthy androgen levels and SHBG balance.
Oily fish (salmon, mackerel, sardines)
Rich in omega-3 fatty acids, which support reduction of systemic inflammation — a factor linked to suppressed testosterone production — and may modestly support SHBG normalisation.
Eggs
Provide cholesterol, which is the direct precursor for steroid hormone synthesis including testosterone; dietary cholesterol from whole foods does not adversely affect hormone balance in most people.
Zinc-rich foods (meat, shellfish, legumes, seeds)
Zinc is required for testosterone synthesis and for normal pituitary LH secretion; deficiency is associated with reduced testosterone, and adequate dietary intake supports normal levels.
Cruciferous vegetables (broccoli, cauliflower, Brussels sprouts)
Contain indole-3-carbinol, which supports healthy oestrogen metabolism in the liver and may help maintain a favourable androgen-to-oestrogen balance.
Whole grains and legumes
High-fibre diets are associated with lower insulin resistance and healthier SHBG levels, supporting appropriate free testosterone balance — particularly relevant when low SHBG is a concern.
Track your own Free Testosterone
Upload a lab PDF and Better Days trends Free Testosterone over time, flags it when it drifts, and suggests foods that help.
More in Hormones
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.