Testosterone Levels by Age: What's Normal in the UK

1. What does testosterone actually do?

Testosterone is the primary androgen in both men and women. In men, it's produced mainly by the Leydig cells in the testes, regulated by luteinising hormone (LH) from the pituitary gland. Women produce smaller quantities in the ovaries and adrenal glands.

Beyond muscle mass and sex drive, testosterone regulates bone density, red blood cell production, fat distribution, mood, and cognitive function. Low levels are associated with increased cardiovascular risk, type 2 diabetes, osteoporosis, and depression — not just “feeling a bit tired.”

The challenge isn't whether testosterone matters. It's that the reference ranges used by most UK labs are so wide (6–27 nmol/L in some NHS labs) that a 25‑year‑old athlete and a 75‑year‑old with metabolic syndrome can both be told they're “normal.” Understanding what your level means for your age is the first step.

2. Normal testosterone levels by age (nmol/L)

The table below shows total testosterone reference ranges for men, based on data from the British Society for Sexual Medicine (BSSM) and UK laboratory standards. All values are in nmol/L — the standard unit used by UK labs.

Note that NHS lab ranges vary. North Bristol NHS Trust uses 6–27 nmol/L. Other trusts use 8.7–29 nmol/L. This inconsistency is itself a problem — a man at 7 nmol/L could be flagged as low at one hospital and “normal” at another. This is why clinical context matters more than the number alone.

3. Does testosterone really decline 1% per year?

You'll read everywhere that testosterone drops 1–2% per year after 30. It's repeated so often it's treated as biological law. But the evidence is more nuanced.

A 2014 study published in the European Journal of Endocrinology built validated age-specific reference ranges from healthy men and found no significant decline in total testosterone after age 40 in men who remained healthy, non-obese, and free of chronic illness. The observed population-level decline is largely driven by rising rates of obesity, type 2 diabetes, and medication use — not ageing itself.

This matters because it reframes the conversation. If your testosterone is 11 nmol/L at 45, the answer isn't necessarily “that's just ageing.” It may be that your body composition, sleep, or metabolic health is driving the decline — and those are modifiable.

The BSSM 2023 guidelines agree: “The decline in testosterone with ageing is predominantly explained by comorbidities, particularly obesity.”

4. Free testosterone vs total: which matters more?

Total testosterone measures everything in your blood — but only 2–3% of it is “free” (unbound and biologically active). The rest is bound to SHBG (sex hormone-binding globulin) (~60–70%) or albumin (~30–40%).

Here's why this matters in practice: a man with total testosterone of 15 nmol/L and SHBG of 20 nmol/L has plenty of free testosterone available. The same total T with SHBG of 60 nmol/L means most of that testosterone is locked up and inactive — he could have genuine androgen deficiency symptoms despite a “normal” total T reading.

The BSSM recommends measuring free testosterone when total T is in the grey zone (8–12 nmol/L) or when SHBG is suspected to be abnormal. A free testosterone below 0.225 nmol/L is considered low.

Conditions that raise SHBG (and therefore lower free T): ageing, hyperthyroidism, liver disease, anticonvulsants, and oestrogen therapy. Conditions that lower SHBG: obesity, type 2 diabetes, hypothyroidism, and anabolic steroid use. This is why testing SHBG alongside testosterone gives a far more complete picture than total T alone.

5. The grey zone: 8–12 nmol/L explained

The BSSM practical guidelines define three clinical thresholds for total testosterone:

The grey zone is where most men who “feel low T” will land — and where most GPs will say “it's normal.” Understanding this clinical framework lets you have an informed conversation with your doctor rather than accepting a dismissive “it's fine.”

6. At what testosterone level do symptoms appear?

Symptoms don't suddenly appear at a single threshold. They emerge progressively as levels fall. Based on clinical data cited in the BSSM 2023 review:

These thresholds are approximate and individual variation is real. Some men function well at 12 nmol/L; others feel terrible at 16. This is exactly why baseline testing in your 20s or 30s is valuable — if your personal level was 25 and it's now 14, that's a significant relative decline even if the absolute number is “normal.”

7. What tanks your testosterone (and it's not just age)

If the “1% per year” decline is largely driven by lifestyle and health status, what specifically causes it? These are the most significant modifiable and medication-related factors:

8. When and how to test (timing matters)

Testosterone follows a circadian rhythm: it peaks between 7–10am and can be 30% lower by late afternoon. If your blood was drawn at 4pm, your result could be significantly understated.

The BSSM guidelines are specific: testosterone should be measured from a fasting morning blood sample, ideally before 10am. A single low result must be confirmed with a repeat test at least 4 weeks later — levels fluctuate day to day and a single snapshot isn't diagnostic.

What to request (or what your test should include):

• Total testosterone — the headline number
• SHBG — to calculate free testosterone
• Free testosterone (calculated or measured) — the biologically active fraction
• LH and FSH — to distinguish between primary (testicular) and secondary (pituitary) causes
• Prolactin — elevated levels suggest pituitary pathology
• Thyroid function (TSH) — thyroid disorders mimic low-T symptoms

Our Performance panel includes testosterone, SHBG, cortisol, and DHEA-S alongside inflammatory and metabolic markers — giving you the context needed to interpret your testosterone result properly.

9. What happens if your levels are low? The UK pathway

If you go to your GP with suspected low testosterone, here's the typical NHS pathway:

1. Initial blood test — total testosterone, usually at the GP surgery. Many GPs don't specify morning/fasting, which can produce a falsely low result.
2. Repeat blood test — if the first is low, a confirmatory fasting morning sample is requested 4–6 weeks later. LH, FSH, prolactin, and thyroid function should be included.
3. Endocrinology referral — if confirmed low, you're referred to an endocrinologist. Current NHS wait times: 3–6 months in most areas.
4. Treatment decision — if TRT is indicated, options include testosterone gel (Testogel/Tostran), injections (Sustanon or Nebido), or patches. Treatment is lifelong and affects fertility.

The gap between step 1 and treatment can be 6–12 months on the NHS. This is one reason men opt for private blood testing — not to self-prescribe TRT, but to arrive at the GP appointment with comprehensive, correctly-timed blood results that remove ambiguity and speed up the referral pathway.

10. Testosterone in women: the overlooked hormone

Testosterone isn't just a male hormone. Women produce it in smaller quantities, and it plays a critical role in energy, libido, bone density, and mood. Women's testosterone is often overlooked because the reference ranges are narrow and many GPs don't routinely test it.

NICE menopause guidance (NG23) now recommends that testosterone supplementation can be considered for menopausal women with low sexual desire when HRT alone hasn't worked. No testosterone products are currently licensed for women in the UK — all prescribing is off-label, which is one reason many GPs won't initiate it.

On the other end, elevated testosterone in women is one of the diagnostic criteria for polycystic ovary syndrome (PCOS), which affects approximately 1 in 10 women in the UK.

11. How to raise testosterone naturally (what actually works)

Before considering TRT, these interventions have genuine clinical evidence behind them. They're listed in order of effect size:

Frequently asked questions