Testosterone does not fall off a cliff at menopause and it does not suddenly disappear in your 40s. According to a study just published in the Journal of Endocrinological Investigation out of University College London, testosterone declines at a steady, linear rate of approximately 1.4% per year starting in your 20s.
By the time perimenopause begins, a significant portion of that decline has already happened. And for most women, nobody has ever checked it, contextualized it, or connected it to how they feel and this study changes that conversation.
Why 1.4% Per Year Matters
A 1.4% annual decline sounds small. But compounded across two decades, it is not.
A woman at 25 with a median testosterone of approximately 36 ng/dL will, by age 45, have a median of approximately 24 ng/dL, a reduction of roughly one third, simply from the passage of time, with no surgery, no illness, no dramatic hormonal event. Just the slow, steady, mathematically predictable decline the study documents.
This is why women in their late 30s and early 40s describe losing something they cannot quite name. Energy that used to be there. Motivation that has quietly faded. A body that no longer responds to exercise the way it once did. Libido that has gradually, imperceptibly disappeared. These are not personal failings or signs of stress. They are, at least in part, the clinical consequence of a decade or more of steady testosterone decline.
What the Study Did
Researchers at UCL analyzed testosterone levels in 5,323 women aged 19 to 59. Samples were collected on day 3 of the menstrual cycle, after an 8-hour fast, through the same lab using the same assay. Women were excluded for PCOS, irregular cycles, abnormal BMI, hormonal contraceptive use, and hirsutism. From this carefully screened dataset, the researchers built an age-continuous reference range, the first of its kind at this scale, modeled at each specific year of age.
The result is the most robust age-specific female testosterone data currently available. And it allows us to do something that has never been possible before with this level of precision: compare a woman's testosterone not to a broad range built from women 20 to 30 years younger or older than her, but to women her own age.
The Numbers By Age
The study reports values in nmol/L. Here they are converted to ng/dL, the unit most commonly reported by US labs:
Ages 20 to 25: median 34 to 38 ng/dL, low end of normal around 12 to 14 ng/dL
Ages 25 to 30: median 31 to 34 ng/dL, low end of normal around 10 to 12 ng/dL
Ages 30 to 35: median 28 to 31 ng/dL, low end of normal around 8 to 10 ng/dL
Ages 35 to 40: median 25 to 28 ng/dL, low end of normal around 7 to 8 ng/dL
Ages 40 to 45: median 23 to 25 ng/dL, low end of normal around 6 to 7 ng/dL
Ages 45 to 50: median 20 to 23 ng/dL, low end of normal around 5 to 6 ng/dL
Ages 50 to 58: median 18 to 21 ng/dL, low end of normal around 4 to 5 ng/dL
Look at the progression. From the early 20s to the late 50s, median testosterone drops from approximately 37 ng/dL to approximately 18 ng/dL. That is a reduction of more than 50% across a woman's adult reproductive lifespan, happening quietly, gradually, and almost entirely beneath the radar of routine medical care.
The Problem With Current Lab Reference Ranges
The most widely used reference range for female testosterone, from Roche, one of the leading lab suppliers, was established from a study of just 149 women, split into two broad age groups: 20 to 49 years old and 50 and over. One number covers three decades of hormonal life. No age-specific breakdown within those groups. No accounting for the fact that a 28-year-old and a 48-year-old have fundamentally different testosterone physiology.
This means that when your lab report says your testosterone is within the normal range, it is comparing you to a population that spans 30 years and was built from fewer than 150 women.
The clinical consequence is significant. A woman who is 43 with a testosterone of 7 ng/dL will likely be told her result is normal. But this study shows she is in the bottom 2.5% for her age group. That is not normal for a 43-year-old. That is significantly low. And the symptoms she may be experiencing, low energy, poor libido, difficulty building muscle, cognitive flatness, deserve to be investigated and treated accordingly.
What Symptoms Look Like Along the Decline
Because the decline is gradual, the symptoms tend to be gradual too. Women rarely wake up one day and recognize testosterone deficiency. Instead they notice small, incremental changes over months and years.
Energy that used to carry them through a busy day begins to feel unreliable. Motivation and drive, what many describe as their internal spark, becomes harder to access. Libido shifts from a natural baseline to something that requires effort or simply disappears. Muscle tone becomes harder to maintain even with consistent exercise. Cognitive sharpness, confidence, and emotional resilience all subtly change. And because these changes are gradual and overlap completely with the symptoms of stress, burnout, and perimenopause, they are almost universally attributed to something else.
This is exactly why the 1.4% annual decline is so important to understand. The changes are not happening to you all at once. They have been accumulating for years. And by the time a woman seeks help, she is often looking at a decade or more of unrecognized testosterone loss.
The Limitations
This study is the most rigorous age-specific female testosterone data currently published but it has limitations worth knowing.
It is a UK-based population, 83.7% white. Women were self-selected, having purchased private at-home hormone testing, which likely skews toward more health-conscious and possibly more symptomatic individuals. Blood was collected via finger prick rather than venous draw. And the assay used was immunoassay rather than LC-MS/MS, which is the gold standard method for testosterone measurement in women.
These limitations do not invalidate the findings. They contextualize them. The data is significantly more robust than what most labs currently use and it moves clinical practice meaningfully forward. But validation in more diverse populations and with LC-MS/MS methodology would strengthen the findings considerably.
What This Means at The Lee Clinic
We check testosterone in every patient, but understand that you are more than just a number. Symptoms of low testosterone can arise, even if your numbers are "normal".
The 1.4% annual decline this study documents is exactly why we do not wait for a woman to reach menopause before asking these questions. The decline is already underway in her 20s. By her late 30s it is measurable. By her mid-40s it is often clinically significant. And connecting it to how she actually feels, her energy, her drive, her body composition, her cognitive clarity, is part of what comprehensive hormone care looks like.
If your testosterone has never been checked, or if you have been told it is normal without anyone comparing it to women your age or asking about your symptoms, that conversation is worth having.
It is one we are ready to have with you.
The Lee Clinic sees patients in person in Winchester and Reston, VA. Telehealth appointments are available for patients in FL, DC, WV, and MD. Call us at 540-542-1700 to schedule.
Citation: Wainwright E, Getreu N, Crawford L, et al. Redefining testosterone reference ranges for adult females. J Endocrinol Invest. 2026;49:2339-2349. https://doi.org/10.1007/s40618-026-02929-w