One of the most common questions men ask after starting testosterone replacement therapy is deceptively simple: “What should my levels be?” It sounds like it should have a straightforward numerical answer. It doesn’t — and understanding why is one of the most important things you can learn about your treatment.
The truth is that optimal testosterone levels on TRT are not a single number. They’re a personalised target that depends on your symptoms, your blood work, your SHBG levels, when your blood was drawn relative to your last dose, and how your body responds to treatment. Two men with identical blood results can feel completely different — one thriving, the other still struggling.
This article breaks down what the numbers actually mean, what “optimal” looks like in practice, and why chasing a specific number on a lab report can sometimes do more harm than good.
Understanding the Reference Range
Most UK laboratories report a total testosterone reference range of approximately 8.0 to 27.0 nmol/L (230 to 780 ng/dL in American units). This range is derived from population studies of healthy men, typically aged 18 to 40, and represents the statistical spread from the 2.5th to 97.5th percentile.
Here’s the problem: a result of 8.5 nmol/L is technically “within range,” but it sits at the very bottom. A 35-year-old man with a total testosterone of 8.5 nmol/L and symptoms of fatigue, low libido, and brain fog is not “normal” in any meaningful clinical sense — he’s just not flagged as abnormal by the laboratory’s reference range.
Reference ranges tell you what is statistically common. They do not tell you what is optimal for you as an individual. This distinction matters enormously when you’re on TRT and trying to work out whether your dose is right.
What the guidelines say
The British Society for Sexual Medicine (BSSM) guidelines suggest that the aim of TRT is to restore testosterone to the mid-normal range, typically targeting trough levels of around 15 to 20 nmol/L. The European Association of Urology (EAU) offers similar guidance, recommending that levels be maintained within the normal physiological range.
NICE Clinical Knowledge Summaries advise that treatment should aim to relieve symptoms while keeping levels within the normal reference range, with regular monitoring to ensure safety.
None of these guidelines give a single “magic number.” They all emphasise that treatment should be guided by a combination of blood levels and symptom response.
Total Testosterone vs Free Testosterone
Total testosterone measures all the testosterone in your blood, but roughly 98% of it is bound to proteins — primarily SHBG (sex hormone-binding globulin) and albumin. Only about 2-3% circulates freely, and it’s this free testosterone that is biologically active and can enter cells to exert its effects.
This means your total testosterone can look perfectly normal while your free testosterone is genuinely low. This happens most commonly when SHBG is elevated, which binds up more testosterone and leaves less of it available to your tissues.
When free testosterone matters more
Free testosterone becomes particularly important in the following scenarios:
- Your total testosterone is in the “grey zone” (8-15 nmol/L) — Free testosterone can help determine whether you’re truly deficient
- Your SHBG is high — Common in older men, men who are lean, men taking certain medications, and those with liver conditions or hyperthyroidism
- Your total testosterone looks adequate but symptoms persist — Low free testosterone may explain the disconnect
- You’re on TRT and not responding as expected — Checking free testosterone can reveal whether the testosterone you’re replacing is actually bioavailable
A typical target for free testosterone on TRT is within the upper half of the reference range, though this varies by laboratory. Most UK labs report free testosterone in pmol/L, with a reference range of approximately 0.17 to 0.67 nmol/L (or 170 to 670 pmol/L).
The Role of SHBG
SHBG deserves its own section because it’s one of the most underappreciated factors in TRT management. Sex hormone-binding globulin is a protein produced by the liver that binds testosterone with high affinity. When SHBG is high, more testosterone is bound and less is free. When SHBG is low, more testosterone is free.
| SHBG Level | Effect on Free Testosterone | Common Causes |
|---|---|---|
| High (above 50-60 nmol/L) | Reduces free testosterone — symptoms may persist despite “normal” total T | Ageing, low body weight, liver disease, hyperthyroidism, certain medications (anticonvulsants) |
| Normal (20-50 nmol/L) | Total testosterone is a reasonable guide | Normal physiology |
| Low (below 20 nmol/L) | Increases free testosterone — total T may look low while free T is adequate | Obesity, insulin resistance, type 2 diabetes, hypothyroidism, anabolic steroid use |
This is why comprehensive blood testing — not just total testosterone — is essential both for diagnosis and for monitoring on TRT. At Evernu, our testosterone blood test includes SHBG, free testosterone, and a full hormonal panel precisely because these markers are inseparable from the total testosterone reading.
Trough Levels vs Peak Levels: Why Timing Matters
If you’re on injectable testosterone, your blood levels are not constant. They rise after injection and gradually fall until your next dose. The lowest point — just before your next injection — is called the trough. The highest point, typically 24-48 hours after injection, is the peak.
Blood tests for monitoring TRT should be taken at the trough — that is, immediately before your next scheduled injection. This gives your clinician the most useful information: if your trough level is adequate, it means your levels are staying in a good range throughout the entire injection cycle.
If your blood is drawn at peak, your result will be artificially high and won’t tell you whether you’re dipping too low before your next dose. Conversely, if your blood is drawn mid-cycle, the result is hard to interpret without knowing exactly where you are in the cycle.
Trough targets
Most clinicians aim for a trough total testosterone of approximately:
- 15 to 25 nmol/L (some guidelines say 15-20 nmol/L as a starting target)
- Above 12 nmol/L at minimum — if your trough is below this, your dose likely needs increasing
- Below 30 nmol/L — consistently supraphysiological trough levels suggest the dose is too high
For men on daily testosterone gel, levels are more stable throughout the day, and blood should be drawn in the morning, ideally before applying that day’s gel. The same general target ranges apply.
Why “Optimal” Is Personal
Here’s where the conversation gets nuanced. Two men can have identical trough testosterone levels — say 18 nmol/L — and have vastly different symptom profiles. One may feel completely restored: energy returned, libido healthy, mood stable, sleeping well. The other may still feel flat, fatigued, and unmotivated.
Why? Because symptom response depends on more than just the testosterone number:
- Free testosterone may differ due to different SHBG levels
- Androgen receptor sensitivity varies between individuals (genetic variation)
- Oestradiol levels — testosterone converts to oestradiol via aromatase. If oestradiol is too high or too low, symptoms can persist
- Thyroid function — undiagnosed hypothyroidism mimics low testosterone symptoms
- Sleep quality, stress, and lifestyle factors — these profoundly affect how you feel regardless of your testosterone level
- Expectations — TRT treats testosterone deficiency, not life dissatisfaction
This is why good TRT management is never purely about numbers. A skilled clinician will look at the full picture: your blood results, your symptoms, your lifestyle, and your response over time. The goal is to find the dose that gives you the best symptom relief while keeping all your markers in a safe range.
How Clinicians Titrate Your Dose
Dose adjustment on TRT (often called “titration”) is a gradual, methodical process. Here’s how it typically works:
- Start conservatively. Most clinicians begin with a moderate dose — for example, 125mg of testosterone cypionate or enanthate per week, or one sachet of Testogel daily.
- First blood test at 6-8 weeks. This allows levels to stabilise. The blood test should be at trough.
- Assess both numbers and symptoms. If trough levels are low and symptoms haven’t improved, the dose is increased modestly. If levels are high or side effects are present (elevated haematocrit, high oestradiol, acne), the dose may be reduced.
- Repeat at 3-month intervals until a stable, effective dose is found.
- Maintenance monitoring every 6-12 months once stable.
The most common mistake in TRT management is changing the dose too frequently. Testosterone takes time to reach steady state, and adjusting the dose every few weeks based on a single blood test creates instability. We discuss this in detail in our article on TRT protocols and consistency.
The Danger of Chasing Numbers
One of the most counterproductive patterns we see is men who fixate on achieving a specific testosterone number — often one they’ve seen promoted on social media or bodybuilding forums. “I want my levels at 30 nmol/L” or “I won’t feel good until I’m at the top of the range.”
There are several problems with this approach:
- Supraphysiological levels carry risks. Pushing levels above the normal range increases the risk of polycythaemia (elevated red blood cells), which can lead to blood clots. It can also worsen acne, cause mood instability, and raise oestradiol to uncomfortable levels.
- More is not always better. Research consistently shows that symptom improvement plateaus once levels reach the mid-normal range. Going higher doesn’t necessarily produce additional benefit but does increase risk.
- It shifts focus away from what matters. The goal of TRT is to feel well and function normally, not to achieve a specific lab value. If your symptoms have resolved at 17 nmol/L, pushing to 25 nmol/L is unlikely to make you feel appreciably better and may introduce side effects.
The number serves the symptom picture, not the other way round.
What About Oestradiol?
Testosterone is partially converted to oestradiol (a form of oestrogen) by an enzyme called aromatase. This is a normal physiological process, and men need some oestradiol for bone health, cardiovascular function, brain function, and libido.
However, if oestradiol rises too high on TRT, it can cause symptoms such as:
- Water retention and bloating
- Mood changes, irritability, or emotional sensitivity
- Breast tenderness or gynaecomastia
- Reduced libido (paradoxically)
Conversely, oestradiol that is too low (often due to overzealous use of aromatase inhibitors) can cause joint pain, low mood, poor libido, and bone loss.
Monitoring oestradiol as part of your regular blood work ensures it stays in balance. Most clinicians aim for oestradiol within the normal male reference range, adjusting the testosterone dose or injection frequency if oestradiol climbs too high. Aromatase inhibitors are used cautiously and only when necessary — they are not a routine part of well-managed TRT.
Monitoring Schedule on TRT
A typical monitoring schedule looks like this:
| Timepoint | What’s Checked | Purpose |
|---|---|---|
| Baseline (before starting) | Full hormonal panel, FBC, PSA, metabolic markers | Establish baseline, confirm diagnosis |
| 6-8 weeks | Total T, free T, oestradiol, FBC, haematocrit | Check initial response, screen for polycythaemia |
| 3 months | Full panel including PSA | Dose titration, comprehensive safety check |
| 6 months | Full panel | Ongoing optimisation |
| Every 6-12 months (once stable) | Full panel including PSA, FBC, lipids, HbA1c | Long-term safety monitoring |
If you’re not being monitored at these intervals, your TRT is not being managed properly. Monitoring isn’t just about checking testosterone — it’s about ensuring your overall health remains on track.
What Should You Do?
If you’re on TRT and wondering whether your levels are where they should be, here’s our practical advice:
- Get a comprehensive blood test at trough. Not just total testosterone — include free testosterone, SHBG, oestradiol, FBC, and PSA at minimum. Our at-home testosterone test covers all of these.
- Don’t obsess over a single number. Focus on how you feel. If your symptoms have improved significantly and your blood markers are safe, your dose is probably right — even if your total testosterone isn’t at the top of the range.
- Give each dose change time. Don’t judge a new dose based on how you feel after one week. Allow 6-8 weeks for levels to stabilise before reassessing.
- Work with a clinician who understands TRT. Dose optimisation is a clinical skill. You need someone who looks at the whole picture, not just one number on a lab report.
- If you’re not on TRT but suspect low testosterone, start with our free screening questionnaire and explore our testosterone treatment service.
The right testosterone level on TRT is the one where you feel well, your symptoms are resolved, and your health markers are in a safe range. That number is different for every man, and finding it is a collaborative process between you and your clinician.
