Total, Free, Bioavailable: Which Testosterone Number Your Symptoms Follow
Published 10/21/2026
Contents
Key Takeaways
- Total testosterone counts everything in circulation, including the large fraction bound tightly to SHBG and unavailable to tissues.
- Free testosterone is the small unbound fraction, typically a few percent of the total.
- Bioavailable testosterone counts free testosterone plus the loosely albumin-bound portion that tissues can still access.
- Men with low free testosterone but normal total testosterone report more deficiency symptoms than men normal on both.
- Most free testosterone values are calculated rather than measured, and a 15% shift in the SHBG input can change the resulting diagnosis.
Order a thorough testosterone panel and you get three numbers where you expected one. Total, free, and bioavailable. They are not three attempts at the same measurement. They answer three different questions, and when they disagree, the disagreement is the finding.
What Each One Counts
Testosterone does not circulate loose. Most of it is bound to proteins, and binding determines whether a tissue can use it.
Total testosterone counts everything in the sample. Bound, unbound, all of it. It is the cheapest and most commonly ordered measurement, and it is the one almost every man has had.
Free testosterone counts only the unbound fraction, typically a low single-digit percentage of the total. This is testosterone that can enter a cell without anything releasing it first.
Bioavailable testosterone counts free testosterone plus the portion loosely bound to albumin. Albumin holds testosterone weakly enough that tissues can still strip it off, so functionally this fraction remains accessible.
The portion bound tightly to sex hormone binding globulin (SHBG) is the part that is counted in total and excluded from the other two. SHBG holds on with high affinity, and what it is holding is not available to your tissues in any practical sense.
Why They Disagree
Two men can have identical total testosterone and very different amounts of usable hormone, because they are carrying different amounts of SHBG.
SHBG is not fixed. It rises with age. It rises with thyroid overactivity and with liver disease. It falls with obesity, insulin resistance, and type 2 diabetes. Several medications move it. So the proportion of your total testosterone that is actually available shifts with things that have nothing to do with how much testosterone you are producing.
This produces the single most frustrating pattern in men's health: a total testosterone comfortably inside the reference range alongside symptoms that look exactly like deficiency. The research supports the pattern rather than dismissing it. Men with isolated low free testosterone and normal total testosterone report more androgen deficiency signs and symptoms than men who are normal on both measures.
If you have been told your testosterone is fine and you do not believe it, this is the first place to look.
Which Number Tracks How You Feel
The general answer is that free and bioavailable testosterone track symptoms more closely than total does, because they describe what tissues can actually use.
There is measurable support for this beyond symptom reporting. Hematopoiesis, the production of red blood cells, correlates more closely with calculated free testosterone in men than with total testosterone, which is a biological endpoint rather than a questionnaire.
Guideline practice reflects it too. The Endocrine Society recommends measuring free or bioavailable testosterone, by a validated assay, in men whose total testosterone sits near the lower limit of normal or in whom an SHBG abnormality is suspected. Total testosterone remains the right first test; the others are what you add when the first one does not settle the question.
The Honest Caveat About Calculated Values
This is the part that rarely makes it into consumer writing, and it matters for how much weight you put on the number.
Most free testosterone results are not measured directly. The reference method, equilibrium dialysis, is labour-intensive and not routine. What most labs report is a value calculated from total testosterone, SHBG, and albumin using an equation.
Three consequences follow.
The equation choice changes the answer. Several formulae are in use, including Vermeulen, Ly, Sartorius and Sodergard. The Vermeulen equation shows the smallest bias against reference methods, around 2.6%, and is generally the preferred model, but different calculators return different numbers from identical inputs.
The SHBG input carries its own error. SHBG immunoassays vary between laboratories. When researchers simulated interlaboratory SHBG variation by shifting measured values by 15%, the proportion of men classified as deficient changed, and changed differently depending on which formula was used. A calculated value inherits the uncertainty of everything feeding it.
The underlying model is a simplification. The common equations assume linear binding, while detailed biophysical work describes SHBG binding as non-linear and multiphasic. Calculated values can diverge meaningfully from equilibrium dialysis measurements.
None of this makes calculated free testosterone useless. It is informative and it is the practical option. But it is an estimate with a margin, and a result sitting a few percent either side of a threshold should not be treated as a verdict.
How To Read Your Own Panel
A practical order of operations.
Start with total testosterone, measured fasting in the morning and confirmed on a repeat. If it is unambiguously low or unambiguously normal and your symptoms agree, you may not need the rest.
Add SHBG whenever total and symptoms disagree. Without it you cannot interpret anything else, and it frequently explains the discrepancy on its own.
Read free or bioavailable testosterone as a range rather than a point. Note which formula your lab used if it says. Compare like with like over time: same lab, same method, same morning conditions.
Interpret all of it alongside LH and FSH. Those determine whether a genuinely low result originates at the testes or in the signalling, and that is the distinction that decides which treatments are possible.
Frequently Asked Questions
What is the difference between free and total testosterone?
Total counts all testosterone in circulation, including the large fraction bound tightly to SHBG and unavailable to tissues. Free counts only the unbound portion, typically a few percent of the total.
What is bioavailable testosterone?
Free testosterone plus the portion loosely bound to albumin. Albumin releases testosterone readily enough that tissues can still use it, so this fraction is treated as accessible.
Can total testosterone be normal and free testosterone low?
Yes, and it is a common pattern, usually driven by high SHBG. Men in this situation report more deficiency symptoms than men normal on both measures.
Which testosterone number is most accurate?
Total testosterone is the most directly measured. Free testosterone is usually calculated from total, SHBG and albumin rather than measured, so it carries the uncertainty of those inputs and of the equation used.
Should I ask for free testosterone to be measured?
Guideline practice is to add free or bioavailable testosterone when total sits near the lower limit of normal or when an SHBG abnormality is suspected. If your total looks fine and you have persistent symptoms, that is exactly the situation it was meant for.
The Bottom Line
Total testosterone tells you how much you have. Free and bioavailable tell you how much you can use. The second question is usually the one your symptoms are answering.
Just hold the calculated numbers a little loosely. They are estimates built on another measurement, and near a decision threshold that margin deserves respect.
Sources: