Free Testosterone vs Total Testosterone: Why Your Low T Number Might Be Lying
Educational, not medical advice. Interpretation and treatment decisions belong with your clinician.
A plain-English read on why total T can lie, what SHBG is really doing, and how to get an honest free T number.
Total T is the number most labs give you, and the one most likely to fool you
When you get tested, the default is total testosterone: every bit of it in your blood, locked up or not. The big guidelines (Endocrine Society, AUA) still say start there, and that is fine. But total T has a blind spot, and the blind spot has a name: SHBG.
SHBG, in plain English
SHBG (sex hormone binding globulin) is basically a set of handcuffs floating in your blood. Testosterone cuffed to SHBG is locked up. Your body cannot touch it. Testosterone that is free (or loosely riding on albumin) is the stuff that actually gets into your tissues and does the work: libido, energy, mood, muscle.
Your total T counts the cuffed and the free together. Your free T counts only what is actually available. That is the whole ballgame. Two guys with identical total T can feel completely different, because one has a pile of SHBG locking it all up and the other does not.
This is why your number might be lying to you
| Your SHBG | What happens to total T | How you might actually feel |
|---|---|---|
| Low (common with extra weight, insulin resistance, type 2 diabetes) | Reads low | Often better than the number says, because more of what you have is free |
| High | Can read totally "normal" | Low, flat, hypogonadal, because your free T is scraping bottom |
The endocrine societies and recent JAMA reviews call this out specifically for guys carrying extra weight or dealing with insulin resistance: low SHBG drags total T down and makes it look worse than it is. Treating that low total number with TRT can mean treating a number instead of a problem.
How to actually get your free T (and the test to skip)
There are two ways to get a free T number, and they are not equal.
- The cheap one: a "direct" free T immunoassay. Skip it if you can. It is known to be unreliable.
- The good one: calculate it. The Vermeulen equation takes your total T, your SHBG, and your albumin and works out how much is truly free. It is the method clinicians lean on when they cannot run a fancy dialysis test. Run yours in about ten seconds with our free testosterone calculator.
So the move is simple: get total T, SHBG, and albumin on the same blood draw, then calculate free T. That is the honest picture. For the wider panel, see the TRT blood work guide.
Log labs, SHBG, and free T over time
- Smart reminders so you never miss a dose
- Progress tracking with photos and weight
- Medication level curves for every compound
Quick word on "normal" ranges so a lab flag does not freak you out
The standardized total-T range for healthy younger men is roughly 264 to 916 ng/dL. Free T ranges are all over the place depending on how the lab measured it, which is exactly why you want to know whether your free T was calculated or directly measured, and by what method. A free T number with no method attached is close to meaningless.
When free T actually matters
When your total is borderline, or when you have a reason for weird SHBG (extra weight, thyroid, liver). If your total is clearly rock-bottom and you have every symptom, free T is just a formality.
This is the read-your-own-bloodwork stuff, and it is worth understanding so you can ask better questions. But the call to start or change TRT is a medical one. If your labs and how you feel do not line up, that is a conversation with your provider, not a forum thread. Once you have a protocol, the TRT dose calculator is a useful sanity check.
Frequently asked questions
What is the difference between free and total testosterone?
Total is all of it in your blood; free is the small slice not cuffed to SHBG, which is what your body can actually use.
Which one matters more?
Free T tracks how you feel, but you read them together with SHBG. One without the other is half the story.
Why is my total testosterone normal but I feel low?
Usually high SHBG locking up your testosterone, so your free T is low even though total looks fine.
How do I calculate free testosterone?
The Vermeulen equation, using total T + SHBG + albumin. Use our free testosterone calculator.
Ready to track your protocol?
- Smart reminders so you never miss a dose
- Track weight, photos, and progress over time
- Medication level curves for every compound