For adult men aged 18 to 69, a normal free testosterone level falls between roughly 46 and 224 pg/mL, though the range narrows significantly with age. For women, normal levels are much lower, typically between 1 and 6 pg/mL depending on age. These numbers can vary between labs, so the reference range printed on your specific lab report is the one that matters most for interpreting your results.
What Free Testosterone Actually Measures
Only about 2 to 3 percent of your total testosterone circulates freely in the blood. The rest is bound to proteins: most of it locks tightly to a carrier called sex hormone-binding globulin (SHBG), and a smaller portion binds loosely to albumin. The SHBG-bound portion is biologically inactive because SHBG holds onto testosterone too tightly for cells to use it. Free testosterone, the unbound fraction, is the portion that can directly enter cells and do its work.
This is why two people with identical total testosterone levels can feel very different. If one person produces more SHBG, less of their testosterone is available in free form. Measuring free testosterone gives a more complete picture of what your body can actually use, which is especially useful when total testosterone lands in a borderline or ambiguous range.
There’s also a middle category called bioavailable testosterone, which includes both free testosterone and the portion loosely bound to albumin. Because albumin’s grip is weak, that testosterone can still detach and become active. For men aged 18 to 69, bioavailable testosterone typically runs between 110 and 575 ng/dL.
Normal Ranges for Men by Age
Free testosterone peaks in a man’s twenties and declines gradually from there. One widely used reference range from Quest Diagnostics lists 46 to 224 pg/mL as normal for men aged 18 to 69. After age 69, the expected range drops sharply to 6 to 73 pg/mL. Other labs may subdivide age groups differently. UF Health Pathology Laboratories, for example, lists 9.3 to 26.5 pg/mL for men aged 20 to 29, reflecting a different assay method with a much narrower scale.
That discrepancy highlights a critical point: free testosterone reference ranges are not standardized across laboratories. The numbers depend heavily on which measurement technique the lab uses. A result of 15 pg/mL could be perfectly normal on one lab’s scale and borderline low on another’s. Always compare your number to the range printed on your own report rather than to ranges you find online.
Normal Ranges for Women
Women produce far less testosterone than men, and their free testosterone reflects that. Reference values from the University of Iowa break it down by decade:
- Ages 18 to 30: 1 to 5 pg/mL
- Ages 31 to 40: 1 to 6 pg/mL
- Ages 41 to 50: 1 to 4 pg/mL
- Age 51 and older: less than 3 pg/mL
Free testosterone testing in women is most commonly ordered when there are signs of excess, such as acne, unusual hair growth, or irregular periods, which can point to conditions like polycystic ovary syndrome. Low levels may also matter for women experiencing low energy or reduced sex drive after menopause, though the clinical significance is less well established than in men.
Why Testing Method Matters
Not all free testosterone tests are created equal. The gold standard is a technique called equilibrium dialysis, where a lab adds a tracer to your blood sample and lets it pass through a membrane to directly measure the free fraction. This method is accurate but expensive and slow, so many commercial labs use a shortcut called direct analog immunoassay instead. The immunoassay is faster and cheaper, but less precise, particularly at the low end of the range. This is one reason reference intervals vary so dramatically between labs.
A third option skips direct measurement entirely. Some labs calculate free testosterone using a formula that takes your total testosterone, SHBG, and albumin levels and estimates the free portion mathematically. This calculated approach is reasonably reliable when the input measurements are accurate, and it’s what Quest Diagnostics uses in their free and bioavailable testosterone panel. If your lab report lists SHBG and albumin alongside your results, your free testosterone was likely calculated rather than directly measured.
When and How to Get Tested
Testosterone levels follow a daily rhythm. They peak in the early morning, between about 7:00 and 10:00 a.m., and drop to their lowest point in the evening before climbing again overnight. Current guidelines recommend drawing blood between 8:00 and 9:00 a.m. to capture levels near their peak and reduce the effect of this natural fluctuation. A sample taken at 3:00 p.m. could read meaningfully lower than one drawn at 8:00 a.m. in the same person on the same day.
The Endocrine Society recommends diagnosing testosterone deficiency only when levels come back consistently low on at least two separate morning draws, combined with symptoms like fatigue, reduced sex drive, loss of muscle mass, or mood changes. A single low result isn’t enough because day-to-day variation is normal. Illness, poor sleep, stress, and certain medications can all temporarily suppress levels.
What Shifts Your Free Testosterone
Your free testosterone level is shaped by two things: how much total testosterone your body produces and how much SHBG is circulating to bind it up. Anything that raises SHBG effectively lowers your free testosterone even if total production stays the same.
SHBG tends to rise with age, which is one reason free testosterone drops faster than total testosterone as men get older. Liver disease, hyperthyroidism, and certain medications (particularly some anticonvulsants) also increase SHBG. On the other hand, obesity, insulin resistance, and hypothyroidism tend to lower SHBG, which can artificially inflate free testosterone levels even when total testosterone is declining. For men between 18 and 55, a normal SHBG level runs between 10 and 50 nmol/L. After age 55, the range shifts upward to 22 to 77 nmol/L, reflecting the natural age-related increase.
Body composition plays a significant role as well. Excess body fat increases the conversion of testosterone to estrogen through an enzyme found in fat tissue. Losing weight, resistance training, adequate sleep, and managing stress can all support healthier testosterone levels, though these lifestyle changes won’t overcome a true medical cause of deficiency.
Free vs. Total: Which Test Do You Need?
Most clinicians start with a total testosterone measurement because it’s simpler and more standardized. Free testosterone testing adds the most value in specific situations: when total testosterone is borderline (near the low end of normal but not clearly deficient), when SHBG is suspected to be abnormally high or low, or when symptoms don’t match what total testosterone would predict.
For example, an older man with a total testosterone of 400 ng/dL might seem fine on paper, but if his SHBG has risen with age, his free testosterone could be genuinely low. Conversely, an obese man with low total testosterone might have suppressed SHBG, meaning his free testosterone is actually adequate. In both cases, the free measurement tells a more accurate story than total testosterone alone.