Free testosterone levels in adult men typically range from about 6.6 to 26.5 pg/mL, depending on age. For adult women, the normal range is 1.1 to 6.3 pg/mL. These numbers matter because free testosterone is the small fraction of your total testosterone that’s actually available for your body to use, and it can drop even when your total testosterone looks normal on paper.
Reference Ranges for Men by Age
Free testosterone naturally declines as men age, and lab reference ranges reflect this. Based on direct measurement assays, here’s what’s considered normal:
- Ages 20 to 29: 9.3 to 26.5 pg/mL
- Ages 30 to 39: 8.7 to 25.1 pg/mL
- Ages 40 to 49: 6.8 to 21.5 pg/mL
- Ages 50 to 59: 7.2 to 24.0 pg/mL
- Over 59: 6.6 to 18.1 pg/mL
The decline isn’t dramatic decade to decade, but the upper end of the range drops noticeably. A 25-year-old at the top of his range has about 50% more free testosterone than a 65-year-old at the top of his. That gradual slide usually begins somewhere between a man’s 30s and 50s, and it’s considered a normal part of aging rather than a disease.
Reference Ranges for Women
Women produce much less testosterone overall, and their free testosterone range is correspondingly lower: 1.1 to 6.3 pg/mL for adult females. Most labs don’t break this down further by menopause status for the free fraction, even though total testosterone does shift after menopause.
Free testosterone is particularly relevant in conditions like polycystic ovary syndrome (PCOS). In PCOS, insulin resistance drives down the levels of a carrier protein called SHBG, which means more testosterone circulates in its free, active form. A woman with PCOS might have a total testosterone that looks borderline, while her free testosterone is meaningfully elevated and driving symptoms like acne, excess hair growth, or irregular periods.
Why Free Testosterone Differs From Total
Most of the testosterone in your blood isn’t doing anything at any given moment. The majority is bound to a protein called sex hormone-binding globulin (SHBG), and a smaller portion is loosely attached to albumin. Only a small percentage floats freely, unbound, and able to enter cells and activate receptors. That’s your free testosterone.
Usually, free testosterone tracks with total testosterone. If total goes up, free goes up. But several common situations break that pattern. Anything that raises SHBG will lock up more testosterone and lower the free fraction, even if your body is still producing the same amount. Aging does this: men experience a gradual rise in SHBG starting in middle age, which means free testosterone can decline more sharply than total testosterone suggests. Liver disease, hyperthyroidism, and certain medications also raise SHBG.
The reverse happens too. Obesity, insulin resistance, and type 2 diabetes tend to lower SHBG, which can make free testosterone appear relatively higher compared to total levels. This is why clinicians sometimes order free testosterone testing when total testosterone falls in a gray zone, or when a patient has conditions known to shift SHBG.
When “Normal” Total Testosterone Is Misleading
One of the most practical reasons to check free testosterone is that you can have symptoms of low testosterone even when your total levels test within the normal range. A study published in the Journal of Clinical Endocrinology & Metabolism found that men with normal total testosterone but low free testosterone reported more sexual symptoms, including reduced sexual thoughts, erectile dysfunction, and fewer morning erections, compared to men whose free testosterone was also normal. These men also had lower physical function scores, slower walking speed, and more difficulty with vigorous activities and bending.
In other words, free testosterone can be a better reflection of what you’re actually experiencing. If your total testosterone comes back at, say, 400 ng/dL (well within the normal range of roughly 264 to 916), but your SHBG is high and your free testosterone is at the bottom of the range, you might still feel the effects of low androgen activity.
No Universal Cutoff for “Deficient”
Unlike total testosterone, where major medical organizations have settled on a lower limit of about 264 ng/dL as the threshold for deficiency, there is no universally agreed-upon cutoff for free testosterone. The Endocrine Society’s clinical guidelines acknowledge this directly: a harmonized reference range for free testosterone has not been established, so the numbers can vary considerably between labs depending on the method used.
This means the reference range printed on your lab report is specific to that lab’s assay and methodology. You can’t easily compare your free testosterone result from one lab to another, and you shouldn’t fixate on a single number you found online as the definitive line between “healthy” and “low.” What matters more is the combination of your symptoms, your free testosterone level relative to your lab’s specific range, and how your levels track over time.
Testing Methods Affect Your Results
How your free testosterone is measured matters a lot. The gold standard is a technique called equilibrium dialysis, which physically separates the free hormone from the bound fractions. It’s accurate, but it’s expensive, slow, and not available at every lab.
Many labs instead use one of two shortcuts. The first is a calculated estimate, where the lab measures your total testosterone and SHBG, then plugs those into a formula to estimate free testosterone. This is widely used and reasonably reliable, but research shows that at least 25% of samples produce results that deviate unacceptably from the gold standard, regardless of which formula is used. Accuracy tends to be worse at extreme SHBG levels.
The second shortcut is a direct analog immunoassay. The Endocrine Society recommends against using these. They don’t truly measure free testosterone, and their results fluctuate unpredictably with changes in SHBG. If your lab report says “free testosterone, direct” and the number seems off, the test method itself might be part of the problem.
If you’re making treatment decisions based on free testosterone, it’s worth confirming that your lab used either equilibrium dialysis or a well-validated calculation method. Your doctor can tell you which assay was ordered.
Getting an Accurate Test
Testosterone levels peak in the early morning and decline throughout the day. Most guidelines recommend testing in the morning for this reason, and a single low result isn’t enough for a diagnosis. The Endocrine Society specifies that low levels should be confirmed on at least two separate occasions before any treatment decisions are made.
Free testosterone testing is most useful in specific situations: when total testosterone is borderline or near the lower end of normal, when you have symptoms of testosterone deficiency despite a normal total level, or when you have a condition known to alter SHBG (obesity, liver disease, thyroid disorders, or aging). For someone with clearly normal or clearly low total testosterone, free testosterone testing often doesn’t change the clinical picture.