Free vs Total Testosterone: What Each Number Means
Total testosterone is everything in your blood: all the testosterone, whether it is bound to proteins or floating free. Free testosterone is just the small, unbound slice your cells can actually use, and a protein called SHBG decides how big that slice is. That gap matters, because you can have a perfectly "normal" total and still run low on free testosterone, which is why your clinician reads both numbers, not one.
This article explains what these lab values measure and how they relate to each other. It does not diagnose anything or recommend treatment. Testosterone replacement therapy (TRT) is prescription-only in the United States, where testosterone is a Schedule III controlled substance, so the job of interpreting your labs and deciding what, if anything, to do about them belongs to your clinician.
What does total testosterone measure?
Total testosterone measures the entire amount of testosterone in your serum, the liquid part of your blood. That figure includes the testosterone bound to proteins plus the unbound portion, all added together. It is the standard first-line blood test for assessing testosterone, and for most people it is the only one needed.
Labs report this number in one of two units. In the United States you will usually see nanograms per deciliter (ng/dL), a measure of weight per volume of blood. Much of the rest of the world uses nanomoles per liter (nmol/L), which counts molecules instead of weight; roughly speaking, 1 nmol/L is about 28.8 ng/dL, though you should not do mental math on a lab that matters.
The Endocrine Society, a leading professional body for hormone specialists, defines a low total testosterone in its clinical practice guideline as a level below 264 ng/dL (about 9.2 nmol/L). That threshold comes with conditions. The blood should be drawn in the morning, generally between 7 and 11 AM, after fasting, because testosterone naturally peaks early and food can shift the reading.
One low result is not a diagnosis. The Endocrine Society recommends confirming a low value with at least two separate morning measurements, and a diagnosis of low testosterone requires both consistently low readings and matching symptoms. A single number in isolation does not tell your clinician much, which is a theme you will see repeated here.
What does free testosterone measure?
Free testosterone measures only the fraction of testosterone that is not attached to any protein. This is typically a small share of the total, often in the range of 1 to 2 percent. The rest is bound up and held in reserve.
The reason free testosterone gets attention is biology. Only the unbound hormone can readily leave the bloodstream, enter your cells, and act on the tissues that respond to testosterone. In that sense free testosterone is the "active" pool, while the bound portion is more like inventory sitting in a warehouse.
That distinction is why two people with identical total testosterone can feel and function differently. If their free fractions differ, the amount of usable hormone differs, even though the headline number looks the same. Whether that difference is clinically meaningful is, again, a call for your provider.
What binds testosterone in the blood?
Most testosterone in your blood is attached to one of two proteins, and they do not hold on the same way. SHBG (sex hormone-binding globulin) is a protein produced mainly by the liver that binds testosterone tightly. Testosterone locked onto SHBG is essentially held inactive and cannot easily reach your cells.
Albumin, the most abundant protein in blood plasma, also binds testosterone, but loosely. Because that grip is weak, testosterone can come off albumin fairly easily and become available to tissues.
This is where a third term helps. Bioavailable testosterone is defined as the free testosterone plus the albumin-bound testosterone added together, on the logic that both pools can realistically reach your cells. The tightly bound SHBG fraction is left out because it stays locked away. Of these proteins, SHBG is the key variable, because it is the one that swings the most from person to person and pulls testosterone out of circulation.
How does SHBG change the picture?
Because SHBG decides how much testosterone is held inactive, changes in SHBG quietly reshape your free and bioavailable levels even when your total stays put. Several common factors push SHBG up. The Endocrine Society notes that SHBG tends to rise with age, with an overactive thyroid (hyperthyroidism), with certain medications, and with low body fat.
Other factors push SHBG down. Obesity, insulin resistance, and type 2 diabetes are all associated with lower SHBG, which leaves more testosterone unbound relative to the total.
Now picture two men with the exact same total testosterone. The one with high SHBG has more of his hormone locked away, so his free testosterone is lower. The one with low SHBG has more unbound, so his free testosterone is higher. Same headline number, different usable supply.
That scenario, a normal-looking total paired with a genuinely low free testosterone, is exactly the pattern that gets missed when only the total is checked. If you want to see how testosterone fits into a broader hormone and safety panel, our overview of TRT bloodwork and labs walks through the markers clinicians commonly review together.
How do total, free, and bioavailable testosterone compare?
The table below summarizes how the three measures differ. Treat it as orientation, not a scorecard, because the right test depends on your situation and your clinician's judgment.
| Measure | What it measures | What affects it | When it is most useful clinically |
|---|---|---|---|
| Total testosterone | All testosterone in serum, both protein-bound and unbound, added together | Time of day, fasting, illness, overall production, and shifts in binding proteins | The standard first-line test for most people; usually sufficient on its own |
| Free testosterone | Only the unbound fraction (roughly 1 to 2 percent of total) that can enter cells | SHBG level above all, since SHBG holds testosterone inactive | When total is borderline, or when SHBG is suspected to be high or low |
| Bioavailable testosterone | Free plus albumin-bound testosterone, the pools that can reasonably reach tissue | SHBG and albumin levels, which determine how much stays accessible | An alternative to free testosterone when binding proteins are abnormal |
When is free testosterone worth measuring?
For most people the total is enough, and adding more tests just adds noise. The Endocrine Society recommends measuring free testosterone in specific situations: when the total testosterone sits near the borderline, or when there is reason to think SHBG is abnormal and is therefore distorting what the total seems to say.
There is an important catch about how free testosterone is measured, because not all methods are equally trustworthy. The reference, or gold-standard, method is equilibrium dialysis, a laboratory technique that physically separates the unbound hormone. It is accurate but not available everywhere.
Many labs instead use direct or analog immunoassays, which are convenient but are widely regarded as unreliable for free testosterone. A common middle path is calculated free testosterone, which estimates the free fraction using a formula based on your total testosterone, SHBG, and albumin. Each approach has tradeoffs, and which one to order and trust is a decision your provider makes, not something to choose off an internet menu.
How should you read your own numbers?
Carefully, and never alone. Reference ranges differ from lab to lab and from one assay or calculation method to another, so a value flagged "normal" at one lab might read differently elsewhere. Always compare your result against the reference range printed on your own report, not a number you saw online or a friend's results.
Remember that a single lab is a snapshot, not a trend. Testosterone fluctuates across the day and can dip during illness, poor sleep, or stress, which is why the morning, fasting draw and repeat testing exist in the first place. One reading, high or low, rarely settles anything.
It is also worth knowing that symptoms commonly attributed to low testosterone, such as low energy, low libido, or mood changes, overlap with many other causes and are not specific. If your symptoms and your numbers seem to disagree, that is a conversation to have, not a puzzle to solve solo; our piece on the signs of low testosterone covers why symptoms alone cannot confirm the diagnosis. And if you are managing testosterone alongside body-composition goals, reading your hormone trends next to objective body data, like the lean-mass numbers explained in our guide to reading a DEXA scan on GLP-1, gives your clinician a fuller picture than any one test. For broader context on what therapy involves, the TRT basics guide lays out the fundamentals. Across all of it, interpretation stays with your clinician.
Where does Myo fit in?
Myo trends both your free and total testosterone over time, so you can see how each responds to a protocol change instead of reading a single isolated lab in a vacuum. A solitary result tells you where you are on one morning; a line over months tells you which direction things are moving.
The app stores your lab panels and charts your markers in one place, which makes it easier to bring an organized history to your provider for review. Seeing total and free side by side, with their dates and reference ranges attached, is far more useful than digging through a folder of scattered PDFs.
To be clear about the boundaries: Myo is a tracking and education tool. It does not diagnose, it does not prescribe, and it is not a substitute for medical advice. It helps you record and visualize; your clinician does the interpreting and the deciding.
The bottom line
Total testosterone counts every bit of the hormone in your blood, while free testosterone counts only the small unbound fraction your body can actually use, and SHBG is what sets the ratio between them. Because of that, a normal total can sit on top of a low free testosterone, which is why both numbers, read together and confirmed on repeat morning tests, paint a truer picture than either alone. None of this is a diagnosis you can make from a printout: your clinician interprets the labs, the symptoms, and the trend, and decides what they mean for you.
References
- Endocrine Society. "Testosterone Therapy in Men With Hypogonadism" clinical practice guideline. https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy
- Endocrine Society. Hypogonadism patient library. https://www.endocrine.org/patient-engagement/endocrine-library/hypogonadism
- Endocrine Society "Testosterone Therapy in Men With Hypogonadism" clinical practice guideline, on the use of equilibrium dialysis as the reference method and calculated free testosterone (from total testosterone, SHBG, and albumin) as a practical alternative. https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy
Frequently asked questions
What's the difference between free and total testosterone?
Total testosterone measures all the testosterone in your blood, both the portion bound to proteins and the small portion that is unbound. Free testosterone measures only that unbound fraction, which is the part that can enter cells and act. Most testosterone is bound and biologically inactive, so total and free can tell different stories. Your clinician interprets both together.
Which is more important, free or total testosterone?
Neither alone tells the whole story. Total testosterone is the standard first measurement and is usually sufficient, but free or bioavailable testosterone becomes especially useful when the total is borderline or when SHBG is abnormal. The Endocrine Society recommends measuring free testosterone in those situations. This is a clinical judgment your provider makes, not a self-diagnosis.
What is SHBG and how does it affect testosterone?
SHBG (sex hormone-binding globulin) is a protein that binds tightly to testosterone in the blood, holding it inactive. The more SHBG you have, the less testosterone is free to act, even if your total looks normal. SHBG rises with age, certain medications, and conditions like hyperthyroidism, and falls with obesity and insulin resistance. That is why SHBG is central to reading testosterone labs.
Can total testosterone be normal but free be low?
Yes, and it is a commonly missed pattern. If SHBG is high, a large share of your testosterone is bound and inactive, so your total can sit in the normal range while your free testosterone is low. This is one reason guidelines recommend checking free testosterone when symptoms and a normal total do not match. Only a clinician can interpret that combination for you.
What's a normal free testosterone level?
Reference ranges vary by lab and by the assay or calculation method used, so there is no single universal number, and that is exactly why you should not self-interpret. Free testosterone is often reported as a small fraction (roughly 1 to 2 percent) of total. Compare your result against your own lab's reference range and, more importantly, have your provider interpret it alongside your symptoms and other labs.
Keep reading
TRT Bloodwork: The Labs That Get Monitored and Why
TRT bloodwork explained: total and free testosterone, estradiol, hematocrit, PSA, and lipids, what each marker means, and how often they get checked.
Signs of Low Testosterone (and What Actually Confirms It)
Signs of low testosterone: fatigue, low libido, mood and strength changes, and why symptoms alone don't confirm it. What labs actually diagnose low T.
TRT Basics: What Testosterone Replacement Therapy Actually Involves
TRT basics: what testosterone replacement therapy is, who it's for, how it's delivered, the monitoring it requires, and what to realistically expect.