What's a normal testosterone level by age?

There is no single magic number, and that is the first thing to understand about normal testosterone by age. Most labs treat a total testosterone of roughly 300 to 1,000 ng/dL (about 10 to 35 nmol/L) as the adult male range, and many guidelines flag anything below 300 ng/dL as low. That range is deliberately wide, and where a healthy level sits shifts as you get older.

Testosterone usually peaks in the late teens and twenties, then declines slowly, often around 1 per cent a year from the late thirties. So a reading that is perfectly normal at 60 might be a warning sign at 25. The Endocrine Society puts the range for healthy men aged 19 to 39 at 264 to 916 ng/dL, which shows how much normal variation exists even within one age band. Reference ranges also differ from lab to lab, so a figure that reads "low" on one report can sit inside the range on another, which is one more reason not to fixate on a single number.

Three things most men miss when they read a result:

• Timing — testosterone is highest in the morning, so a proper blood test is taken before 10am; an afternoon reading can make a normal man look low
• Free testosterone — the small usable fraction often tells you more than the total, especially when SHBG is high (see what free testosterone is)
• Symptoms — two men with identical numbers can feel completely different

This is why so many men are told their bloodwork is fine yet still feel flat, foggy or low on drive, because the standard panel measures total alone and misses the fuller picture.

What to do: test in the morning, ask for free testosterone and SHBG alongside total, compare your result against an age-appropriate range rather than a single cut-off, and always read the number next to your symptoms (a reading at the top of the range has its own meaning, covered in high testosterone symptoms). One borderline reading is not a diagnosis; a clear pattern across two morning tests, combined with symptoms, is what actually points to low testosterone.