Free vs. Total Testosterone: Understanding the Differences

	Total testosterone	Free testosterone
What it measures	All testosterone in the blood — both bound and unbound	Only the testosterone not attached to proteins, immediately available for the body to use
% of testosterone in blood	100% (the full picture)	~2–3% [1]
Biologically active?	Partially — only the unbound fraction can act on cells	Yes — can enter cells directly to regulate metabolism and cellular function
Normal range (men)	~300–1,000 ng/dL [3]	~46–224 pg/mL (ages 18–70) [3]
Affected by SHBG levels?	Indirectly — high SHBG can make total T appear lower	Directly — high SHBG binds more testosterone, leaving less free T available
When to test	First step when investigating low T symptoms; monitoring TRT	When total T is normal but symptoms persist; when SHBG is abnormal; follow-up testing
What low levels suggest	Possible issue with overall androgen production	Too much testosterone may be bound to SHBG, limiting what's available to the body

It's possible to have a perfectly normal total testosterone level and still experience symptoms of testosterone deficiency—because symptoms aren't driven by how much testosterone your body produces, but by how much is actually available for use. According to some research, free T levels are a better predictor of testosterone deficiency symptoms than total T levels are [1].

The reverse is also true: low total testosterone doesn't always signal a hormone problem. For example, obesity-related insulin resistance can lower SHBG, which causes total testosterone to drop—while free T remains unaffected and within a normal range. So while low total T tells you something may be off with androgen production, low free T can help pinpoint whether excess SHBG is the underlying cause of symptoms.

The unbound testosterone in your bloodstream—the testosterone not attached to SHBG or albumin—is called "free testosterone," or free T. Because it isn't attached to other proteins, free T can enter the body's cells unimpeded to carry out its function as a signaling molecule that regulates metabolism and other cellular functions. Testosterone molecules that are bound to other proteins cannot enter most of your cells.

Free testosterone makes up only about 2–3% of the total testosterone in your blood [1]. The rest is bound—primarily to SHBG, and to a lesser extent to albumin.

It's worth knowing that albumin-bound testosterone is considered "bioavailable," even though it is technically bound. That's because the bond between testosterone and albumin is weak and easily reversible, allowing the hormone to detach and become active relatively quickly. In contrast, testosterone bound tightly to SHBG is not readily available for the body to use. So bioavailable testosterone = free T + albumin-bound T—the combined pool your body can actually draw from.

What affects free testosterone levels?

Because free testosterone is what's left after SHBG and albumin take their share, anything that raises SHBG levels will lower the amount of free T available to your body—even if your total testosterone production stays the same.

Factors that can raise SHBG (and therefore lower free T) include:

• Aging. SHBG levels tend to increase naturally as men get older, which is one reason free testosterone declines with age even when total T remains borderline normal [1].
• Liver disease. The liver produces SHBG, so conditions that affect liver function can elevate SHBG levels.
• Thyroid disorders. An overactive thyroid (hyperthyroidism) is associated with higher SHBG levels.
• Certain medications. Estrogens, some anti-epileptic drugs, and other hormone-affecting medications can raise SHBG.

Factors that can lower SHBG (which may lower total T while free T stays normal) include:

• Obesity and insulin resistance. As noted above, insulin resistance suppresses SHBG production, which can make total testosterone appear lower than it actually is in terms of function.
• Type 2 diabetes. Similarly associated with reduced SHBG levels.

If your SHBG levels are abnormal, testing free testosterone alongside total testosterone gives your provider a much clearer picture of what's actually happening hormonally [3].

Your total testosterone level is a measure of the testosterone concentration you have in your blood in total—both free and bound. (So you'll always have a higher level of total T than free T.)

About 98% of testosterone in the bloodstream is bound to proteins—roughly 40% is bound tightly to SHBG, and the remaining 60% is bound more loosely to albumin [2]. Because SHBG holds testosterone more securely, higher SHBG levels mean less testosterone is free to act in the body. Generally speaking, you'll have lower levels of free T if you have more SHBG.

Total testosterone is typically the starting point. It's the standard first step when investigating symptoms like fatigue, low libido, reduced muscle mass, or erectile dysfunction.

Your healthcare provider may recommend also testing free testosterone if:

• Your total testosterone is low or borderline low
• Your total testosterone is normal, but you still have symptoms of testosterone deficiency
• Your SHBG levels are known to be abnormally high or low
• You are being monitored during testosterone replacement therapy

Testing both together—along with SHBG—gives the most complete picture of your hormonal health and helps your provider understand not just how much testosterone your body is making, but how much of it is actually available for use.

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If you're noticing changes in body fat or muscle mass, shifts in libido, or hair loss, checking your total testosterone is a logical first step. The Everlywell at-home Testosterone Test measures your total testosterone level with a simple finger-prick sample—no lab visit required. Results are delivered on our secure online platform, easy to read and ready to share with your healthcare provider.

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