Testosterone After 40: What Normal Actually Looks Like

Most men over 40 who ask about testosterone have already decided the answer is “low.” That’s usually the wrong place to start. The real data on age and testosterone is messier than the supplement ads make it sound. Getting the right number matters more than just getting a number.

The decline isn’t as universal as it sounds

You’ve probably heard that testosterone drops 1-2% every year after 30. That figure is common, but this post does not have a source for it. A 2014 analysis found a different pattern: in a model built from 13 studies of healthy men (about 10,000 men), average total testosterone fell from the late teens to about age 40 and then did not fall further, while the spread between men grew.^[1] A separate 2023 study of 625 men in the Baltimore Longitudinal Study of Aging (mean age 65) found that once researchers accounted for conditions like obesity, diabetes, and heart disease, age on its own stopped predicting a drop in testosterone. It was an observational study, so it cannot show which way the link runs: illness can lower testosterone, and low testosterone may also contribute to illness.^[2]

In other words: in these studies, health conditions tracked testosterone more closely than age did. That is an association, not a promise that improving body composition, sleep, or metabolic health will raise your number, so ask your clinician what is worth working on.

What “normal” actually means on a lab report

The Endocrine Society, the main group that sets medical guidelines on this topic, published guidance in 2018 that most doctors still follow. It says a diagnosis of low testosterone (called hypogonadism) requires two things together: a consistently low lab number and symptoms.^[3] A low number by itself, with no symptoms, isn’t enough for a diagnosis — and the guideline specifically says doctors shouldn’t screen men who have no symptoms in the first place.

Here’s what that means in practice, before you get tested:

• The guideline calls for repeat fasting morning blood draws, not one afternoon test, and points to the lower limit of your lab’s reference range. Many U.S. clinicians use about 300 ng/dL as a working cut-off, but that number does not come from the guideline cited here.
• You also need symptoms: lower sex drive, unexplained tiredness, loss of muscle, or mood changes. A low number with none of these symptoms usually isn’t something to treat.

Why the symptom-first approach matters

This is the part that “low T” marketing leaves out. Tiredness, low sex drive, and muscle loss at 45 can come from several different causes — poor sleep, chronic stress, thyroid problems, or depression can all look like low testosterone. A blood test exists to figure out which one it actually is, not to confirm a story you’ve already decided is true. If you’re going to get tested, do it because something specific changed for you — not just because you had a birthday.

The actual protocol

1. Track the symptom, not the age. Write down when you noticed a change in libido, energy, or strength — and whether anything else in your life changed at the same time.
2. Get two morning blood draws, not one. Testosterone rises and falls through the day and peaks in the morning. A single afternoon result won’t tell you much.
3. Ask for free testosterone along with total. A protein called SHBG (sex hormone-binding globulin) rises with age and holds on to testosterone, so total testosterone can look normal while the usable (free) amount is low. Free testosterone helps most when your total is near the lower limit.
4. Rule out other causes first. Sleep apnea, uncontrolled diabetes, and obesity all lower testosterone on their own, separate from aging.

None of this means testosterone replacement therapy is the wrong choice for some men. It just means the decision should come from a real diagnostic process — not a feeling that 45 is supposed to feel worse than 35. Treatment has real downsides: it can suppress sperm production and fertility, so tell your clinician if you may want children, and the guideline recommends against starting it in men with certain conditions, which a clinician will check for. Headaches or vision changes, testicular changes, or very low libido with new fatigue need a different work-up, so see a clinician promptly if you notice them.

References

[1] Kelsey TW, Li LQ, Mitchell RT, Whelan A, Anderson RA, Wallace WH. “A Validated Age-Related Normative Model for Male Total Testosterone Shows Increasing Variance but No Decline after Age 40 Years.” PLOS ONE. 2014;9(10):e109346. DOI: 10.1371/journal.pone.0109346. Finding: in a model built from 13 studies of healthy men (n=10,097), average total testosterone fell from the late teens to about age 40 with no further fall afterward, and the variance between men increased with age. ↑︎

[2] Carto CA, Gurayah AA, Arbelaez MCS, Grewal MR, Kohn T, Ramasamy R. Association between comorbidities and longitudinal changes in total testosterone among men from the Baltimore Longitudinal Study of Aging. The Journal of Sexual Medicine. 2023;20(5):605-611. DOI: 10.1093/jsxmed/qdad025. Finding: when adjusted for comorbidities (obesity, diabetes, cardiovascular disease), age does not independently predict a significant decline in testosterone level. ↑︎

[3] Bhasin S, et al. “Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.” Journal of Clinical Endocrinology & Metabolism. 2018;103(5):1715-1744. DOI: 10.1210/jc.2018-00229. Finding: diagnosis requires consistently low testosterone plus symptoms; routine population screening is not recommended. ↑︎

Kurt Greiner

Kurt is a digital strategist and IT professional blending emerging technology with practical application to help businesses and individuals streamline their digital presence. His current work focuses on the intersection of intentional living and technological resilience, exploring how individuals can leverage modern tools to navigate the second half of life with purpose.