Free vs total testosterone: what your results mean

If you’ve ever had a men’s hormone test, you might have seen more than one number on your results. One will say total testosterone. Another might say free testosterone. They sound similar, but they measure different things, and that difference matters.

You could have a “normal” total testosterone level on paper and still feel the classic symptoms of hypogonadism (low testosterone) if your free testosterone is too low. That’s why understanding the difference can be the missing piece in getting the right diagnosis and treatment.¹

The crucial role of testosterone

Testosterone, primarily produced in the testes, is the linchpin of growth, development, fertility, and muscle and bone maintenance. Its reach extends into mood, energy levels, and sexual function. 

Total testosterone is the ‘big’ number

Total testosterone is the overall amount of testosterone in your blood at the time of the test.

It includes:¹

• Free testosterone: the small fraction your body can use immediately

• Bound testosterone:  the larger portion attached to proteins, mainly sex hormone-binding globulin (SHBG) and albumin

Think of total testosterone like your full bank balance. It’s everything you have, both the cash you can spend right now and the money that’s tied up in long-term savings.

On average, around 40–50% of your testosterone is bound tightly to SHBG and can’t be used by your body right away. Another 50–60% is bound more loosely to albumin and can be released when needed. The free testosterone, (like your spending money), makes up only about 2–3% of the total.²

Why does free testosterone matter?

Free testosterone is the testosterone in your bloodstream that’s not bound to proteins. This is the biologically active form that can get to work right away in your tissues.

It’s responsible for:³

• Supporting sex drive and sexual function

• Building and maintaining muscle mass and strength

• Helping with bone density

• Maintaining energy and focus

• Supporting mood and mental clarity

Understanding the gap

Total testosterone levels can be deceiving. High total testosterone may seem impressive, but if most of it is bound by SHBG, it won't yield the same benefits. You'll be the proud owner of a powerful engine without a key – all that potential going to waste. 

High SHBG can happen for several reasons:⁴

• Ageing: SHBG naturally increases with age, which means less free testosterone is available despite having a ‘normal’ total testosterone count

• Certain health conditions: such as liver disease, hyperthyroidism, or HIV

• Medications: like some anti-epileptic or oestrogen-containing drugs

When free testosterone is low, you can experience symptoms of testosterone deficiency even if your total testosterone is “within the normal range.”³

For example, imagine two men both with a total testosterone of 16 nmol/L (which is within the normal range).³

• Man A has low SHBG, meaning a healthy amount of free testosterone is available. He feels energetic, has a normal sex drive, and recovers well from exercise.

• Man B has high SHBG, so his free testosterone is much lower. Despite the same total number, he feels tired, struggles with muscle recovery, and notices a drop in libido.

If we only looked at their total testosterone, we might miss that Man B is showing signs of low testosterone that need further investigation. This may lead to Man B receiving treatment to help supplement the lack of free testosterone in the body, with the aim to treat symptoms they may be experiencing.

Why you should test for both

For many people, total testosterone testing is a good starting point. But free testosterone testing becomes more important if:¹

• Your symptoms suggest low testosterone, but your total result is “normal”

• You have a condition or are on medication known to affect SHBG

• You’re older and noticing changes in mood, energy, or sexual health

• You’re on testosterone therapy, and your clinician wants to fine-tune your dose

The Endocrine Society, the British Society of Sexual Medicine, and other expert guidelines suggest measuring free testosterone when total testosterone is borderline or when SHBG levels may be abnormal.

Normal total testosterone, but still feeling rough? A venous blood test measures free testosterone and SHBG, not just the headline number.

One of the big takeaways from the research is that total testosterone alone doesn’t always tell the full story. A 2020 review found that symptoms and outcomes often correlate better with free testosterone than total levels in certain situations, particularly when SHBG is altered.⁵

That means testing both can help your clinician make a more accurate diagnosis, avoid over- or under-treating, and tailor a treatment plan that’s right for you.

How to raise your free testosterone

Free testosterone responds to the same things that move total testosterone, with one extra lever: anything that lowers SHBG leaves more testosterone unbound and available to your tissues.

Train, and keep training. Resistance work and interval training both raise testosterone acutely, and staying active across months matters more than any single session.⁶

Get your weight into a healthier range. Excess body fat raises aromatase activity, which converts testosterone into oestrogen, and obesity is one of the most consistent predictors of low testosterone in men.⁷ Losing weight is also one of the more reliable ways to bring SHBG and free testosterone back into balance.

Protect your sleep. Most of your daily testosterone is produced while you sleep, and short or broken sleep measurably lowers it.⁸ Seven to nine hours is the target.

Keep an eye on alcohol. Heavy drinking suppresses testosterone production directly.⁹ Moderate intake matters less, but sustained heavy drinking is worth addressing.

Eat enough, and eat well. Zinc, vitamin D, and adequate healthy fat all feed into testosterone production, and very low-fat or heavily restricted diets can work against you.

Then actually measure it. Lifestyle changes are worth making either way, but they will not tell you whether your free testosterone is genuinely low. A blood test will.

The numan take

If your symptoms don’t match your lab results, make sure you've checked your free testosterone. It could be the missing clue that explains why you’re not feeling your best, and it could be the first step towards a plan that works for you.

References

1. ^{Liu Z, Liu J, Shi X, Wang L, Yang Y, Tao M, et al. Comparing calculated free testosterone with total testosterone for screening and diagnosing late-onset hypogonadism in aged males: A cross-sectional study. Journal of clinical laboratory analysis. 2017;31(5).}

2. ^{Yang Q, Li Z, Li W, Lu L, Wu H, Zhuang Y, et al. Association of total testosterone, free testosterone, bioavailable testosterone, sex hormone-binding globulin, and hypertension. Medicine. 2019;98(20): e15628.}

3. ^{Lolck KV, Alcazar J, Kamper RS, Haddock B, Hovind P, Dela F, et al. Compared to total serum testosterone, calculated free testosterone has a stronger association with lean mass, muscle strength, power, and physical function in older men. Aging clinical and experimental research. 2025;37(1): 203.}

4. ^{Gyawali P, Martin SA, Heilbronn LK, Vincent AD, Jenkins AJ, Januszewski AS, et al. Higher serum sex hormone-binding globulin levels are associated with incident cardiovascular disease in men. The journal of clinical endocrinology and metabolism. 2019;104(12): 6301–6315.}

5. ^{Winters SJ. SHBG and total testosterone levels in men with adult onset hypogonadism: what are we overlooking? Clinical diabetes and endocrinology. 2020;6(1): 17.}

6. ^{Riachy R, McKinney K, Tuvdendorj DR. Various factors may modulate the effect of exercise on testosterone levels in men. J Funct Morphol Kinesiol. 2020;5(4):81.}

7. ^{Fui MNT, Dupuis P, Grossmann M. Lowered testosterone in male obesity: mechanisms, morbidity and management. Asian J Androl. 2014;16(2):223-31.}

8. ^{Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011;305(21):2173-4.}

9. ^{Smith SJ, Lopresti AL, Fairchild TJ. The effects of alcohol on testosterone synthesis in men: a review. Expert Rev Endocrinol Metab. 2023;18(2):155-66.}