What's the difference between free and total testosterone?

Total testosterone is all the testosterone in your bloodstream — about 98% of which is bound to proteins (mostly SHBG and albumin) and biologically inactive. Free testosterone is the small fraction (1-2%) circulating unbound and able to enter cells and act on receptors. Free T is what your body actually 'feels.' Total T can look normal while free T is functionally low if SHBG is elevated.

Which matters more, free or total testosterone?

Both, but free testosterone is more clinically relevant for symptoms. A man with normal total T (e.g., 600 ng/dL) but high SHBG can have low free T and low-T symptoms. A man with low-normal total T but normal SHBG can have adequate free T and feel fine. Always look at both numbers together — and ideally also bioavailable testosterone.

What is SHBG and how does it affect testosterone?

Sex hormone binding globulin (SHBG) is the protein that binds most circulating testosterone, making it inactive. High SHBG (often from aging, hyperthyroidism, liver issues, or some medications) reduces free testosterone even when total is normal. Low SHBG (from obesity, insulin resistance) increases free T but is also a sign of metabolic problems.

What's a normal free testosterone level?

Normal free testosterone in adult men is typically 50-200 pg/mL (or 4.5-24 ng/dL depending on assay). Values vary substantially by lab method (calculated vs direct measurement), so always interpret in your specific lab's reference range. The Endocrine Society considers free T below 65 pg/mL low when accompanied by symptoms.

Education Published April 18, 2026

Free Testosterone vs Total Testosterone: What Actually Matters on Your Bloodwork

You got your labs back. Total testosterone says 520 ng/dL, which the lab flagged as "normal." But you still feel tired, foggy, and flat. Here's the part your doctor might not have explained: total T is only half the story. The number that usually tracks with how you actually feel is free testosterone, and most basic panels don't even measure it.

The Two Numbers, Explained

When testosterone is made in the testes, it gets dumped into the bloodstream. From there, it doesn't float around freely for long. Most of it binds to proteins that act like taxis, carrying it through circulation. Only a small fraction stays unbound and chemically free to enter cells and do its job.

Total testosterone measures all of it. Every single molecule in a blood draw, whether it's bound up in traffic or actually available to your tissues. That's the headline number on a standard panel, and the reference range most labs use (roughly 300 to 1000 ng/dL in adult men) is based on it.

Free testosterone measures just the unbound fraction. In most men it's about 1 to 2% of total. It typically gets reported in pg/mL or as a percentage, with normal ranges usually in the 50 to 200 pg/mL area depending on the lab and age.

Why Free T Is the One That Matters

Hormones only work when they can bind to a receptor. Bound testosterone can't do that. It's chemically locked up by a carrier protein, essentially in storage. Only the free fraction can slip into a cell, bind to an androgen receptor, and trigger the downstream effects you actually want: libido, energy, muscle protein synthesis, mood, cognition.

This is why two men with identical total T numbers can feel completely different. Guy A has a total T of 600 and a free T of 140 pg/mL. He feels great. Guy B has a total T of 600 and a free T of 65 pg/mL. He feels like garbage. Same "normal" total, very different biology.

Symptoms correlate more tightly with free T than total T in multiple clinical studies. The classic pattern: normal total, low free, real symptoms. Doctors who only look at total T miss this entirely and tell the patient everything is fine.

Meet SHBG: The Protein That Controls the Whole Thing

The main reason free T can diverge from total T is a protein called sex hormone-binding globulin, or SHBG. SHBG binds tightly to testosterone and holds it out of circulation. About 40 to 60% of your total testosterone is bound to SHBG at any moment. That chunk is effectively inactive.

Another 40 to 55% is loosely bound to albumin. Albumin binding is weak, so that fraction can come off relatively easily and enter tissues. This is why "bioavailable testosterone" (free plus albumin-bound) is sometimes used as a middle-ground measure.

Only the last 1 to 2% is truly free.

Here's the kicker: SHBG is not a fixed number. It rises with age, with low body fat, with thyroid excess, with liver issues, and especially with certain medications. It falls with obesity, insulin resistance, type 2 diabetes, and hypothyroidism. When SHBG rises, it gobbles up more of your testosterone and your free T drops, even if your total T stays the same.

This is exactly why a lot of otherwise healthy lean men in their 40s and 50s end up with normal total T but low free T. Their SHBG drifted up with age, and the fraction that's actually available to their cells dropped.

Bioavailable Testosterone: The Third Option

Some labs report a number called bioavailable testosterone. This is free T plus albumin-bound T. The reasoning is that the albumin bond is weak enough that albumin-bound testosterone can also reach tissues, so counting it gives a more accurate picture of what's actually usable.

In practice, bioavailable T and free T tell a similar story, and they usually move together. If free T is low, bioavailable T is usually low too. If you can only get one, calculated free T from a full panel (total T, SHBG, albumin) is the most commonly used option.

Why Labs Don't Test Free T by Default

Two reasons. One is cost. Measuring free T accurately is harder and more expensive than measuring total T. The gold standard method is equilibrium dialysis followed by mass spectrometry, which is slow and pricey. Most labs instead use cheaper direct immunoassays that are known to be inaccurate, or they calculate free T from total T, SHBG, and albumin. Calculated free T is generally considered more reliable than direct assays.

The second reason is inertia. Total T is what doctors have been trained to look at for decades. Guidelines historically anchored on it, insurance reimbursement revolves around it, and a lot of primary care physicians still treat it as the only number that matters. If you don't specifically ask for free T or SHBG, you probably won't get them.

What to Ask For

When you go in for testosterone-related labs, ask for a full panel, not just total T. At minimum, request:

Total testosterone (standard, always included)
Free testosterone (calculated, preferably, not direct immunoassay)
SHBG (needed to calculate free T and to understand why it's high or low)
Albumin (also needed for calculated free T; often already on a basic metabolic panel)
LH and FSH (help tell you whether low T is coming from the testes or from the brain)

If your doctor pushes back, it's reasonable to explain that you want to understand the bioavailable fraction, not just total. A good endocrinologist or urologist will not blink at this request. If yours does, consider getting a second opinion. Plenty of direct-to-consumer lab services will run a full panel without a referral.

How to Read the Results

Once you have the numbers, look at the pattern, not just individual values.

Normal total, normal free: You're probably fine. If you still have symptoms, look at thyroid, vitamin D, sleep, and mental health.

Low total, low free: Classic low T. Worth a conversation with a doctor about causes and treatment options.

Normal total, low free, high SHBG: Common in lean older men. Symptoms are real even though total looks fine. Options include addressing SHBG drivers (thyroid, liver, certain meds) or discussing treatment with a specialist.

Low total, normal-ish free, low SHBG: Often seen with obesity, insulin resistance, or metabolic syndrome. The path forward is usually weight loss and metabolic health before jumping to TRT.

For more detail on reading a full panel, see our guide on how to read testosterone bloodwork.

A Note on Timing and Variability

Testosterone fluctuates throughout the day. Levels peak in the morning and drop through the afternoon, sometimes by 20 to 30%. A single draw at 3pm is not a good read. Get your blood drawn between 7am and 10am, fasted, and ideally on two separate occasions before drawing conclusions. Free T fluctuates with total T, so the same timing rules apply.

Quick Takeaways

Total T measures all testosterone in your blood. Free T measures the roughly 1 to 2% that's biologically active.
Symptoms track more closely with free T than total T. Normal total with low free is a real thing and often missed.
SHBG binds up 40 to 60% of your testosterone. It rises with age and falls with obesity, changing how much is free.
Bioavailable T (free plus albumin-bound) is a third option and usually moves with free T.
Ask for total T, free T, SHBG, and albumin together. Draw between 7am and 10am, fasted, twice if possible.

Not medical advice. Lab interpretation depends on your full clinical picture. Talk to a qualified physician, ideally an endocrinologist or urologist, before making decisions based on your bloodwork.