Last updated on July 9, 2026
Testosterone is not a fixed number. It rises and falls throughout the day, having its own rhythm, which means the timing of your blood draw can change the appearance of your lab results.
I recently had another blood test. My total testosterone has remained almost constant since the previous test. Optimal, but still in the lower range of optimal. However, I was feeling better going into this rep, so I was expecting a bigger number than I got.
This got me thinking. I did this test a bit later in the day (11am) compared to the original (8am) as that was the time available. I knew that testosterone peaks in the morning and then drops during the day.
But how fast? How much did that matter exactly? Was the later time responsible for 20 points less or over 100 points less? Since I wake up around 5am, was this also a problem with testosterone peaking earlier than most, followed by a drop?
When I asked these questions, I decided I needed to dive into research to answer them.
Testosterone has a daily rhythm
In men, testosterone generally follows a daily pattern, often with higher levels earlier in the day and lower levels later. This daily rhythm has been documented in many studiesalthough the magnitude of the rate varies with age, health status, and individual biology. This chart shows it very well.
As you can see, the effect tends to be much more pronounced in young versus older men.
In short: testosterone is usually not the same at 8am, 11am, 2pm. and 5 p.m.
What happens between morning and afternoon?
A useful study looked at testosterone measurements during normal clinic hours in men. Blood samples were collected at both morning and afternoon visits. The researchers found that testosterone showed enough variation to affect clinical interpretation and concluded that testosterone testing should be limited to morning hours in both younger and older men.
Some of the men had normal testosterone in the mornings, but low testosterone (values below 300 ng/dL) in the afternoon.
Another study found that total testosterone levels measured between 8 A.M. and 11 a.m. averaged 411.7 ng/dL, while levels measured outside this window averaged 368.3 ng/dL. That’s about fifty points, in this case about 25%, between morning and afternoon.
Overall, most studies often show a 10-25% change from the average level in the highs and lows over a 24-hour period.
Examples:
- At 300 ng/dL, a 10–25% swing could be around 30–75 ng/dL.
- At 500 ng/dL, a 10–25% swing could be around 50–125 ng/dL.
- At 900 ng/dL, a 10–25% swing could be around 90–225 ng/dL.
A study found even 25-45% less testosterone at 4:00 p.m. compared to 8:00 A.M. [6]
But pay attention to the shade. The biggest differences occur when morning is compared to later afternoon or evening, not necessarily when comparing 8am. with 11 a.m. So, with this time frame, the declines would be smaller.
Age changes the pattern
In younger men, testosterone tends to exhibit a stronger circadian rhythm. In older men, this rate may slow. A study comparing healthy young men with healthy older men found that young men showed a significant circadian rhythm in non-SHBG-bound testosterone, while the rhythm in older men was much smaller and less consistent.
Men aged 30-40 saw a 25% change in testosterone levels from 8am to 4pm. Men in their 70s saw 10% changes respectively.
Another study found that the early morning testosterone surge observed in young men was significantly reduced or absent in healthy older men.
This means that a younger man may see a larger swing from morning to later in the day, while an older man may have a flatter pattern.
What about other hormones?
Tests found that many other sex hormones were more consistent in men of all ages in multiple studies. These included:
- DHT or dihydrotestosterone
- SHBG
- LH
- FSH
- Estradiol
The weak androgen, DHEA, follows a similar pattern to testosterone.
Cortisol is its own separate topic. This is best checked with four saliva samples during the day for this reason.
What else can change testosterone between tests?
Of course, time is only one variable. Testosterone can also be affected by:
- Sleep quality
- Calorie restriction
- Recent illness
- Alcohol
- Hard training
- Overtraining
- Acute stress
- Laboratory variability
- Medicines
- Sex life
- And many other possibilities
This is why a single testosterone result should not be treated as the final word.
The cleanest way to compare testosterone labs
If you want the most accurate comparison, test under similar conditions. Ideally:
- Test at the same time of day
- Use an early morning draw
- Keep a similar sleep schedule
- Use the same lab if possible
- Avoid hard training immediately before
- Do not take tests during acute illness
- Keep the fasting state stable
This doesn’t make the test perfect, but it does remove obvious noise from the comparison.
Overall, I probably lost some points by doing it slower than usual, but not a huge difference. If I was there at 8am then I might have seen 750-775.
What I do know is that the next time I test, I will make sure to test as soon as possible.
References:
- Tenover, JS, & Bremner, WJ (1991). Circadian rhythm of serum immunoreactive inhibition in young and old men. Journal of gerontology, 46(5), M181–M184. https://doi.org/10.1093/geronj/46.5.m181
- Brambilla et al., The Effect of Diurnal Variation on Clinical Measurement of Serum Testosterone and Other Sex Hormone Levels in Men. The study found clinically relevant diurnal variation in testosterone and concluded that testosterone measurements should be limited to the morning hours in both young and older men. https://academic.oup.com/jcem/article-abstract/94/3/907/2596608
- Plymate, Tenover, and Bremner, Circadian variation in testosterone, sex-hormone-binding globulin, and estimated non-sex-hormone-binding testosterone in healthy young and elderly men. This study found significant circadian rhythm in young men, blunted in older men. https://pubmed.ncbi.nlm.nih.gov/2592266/
- Crawford et al., Testosterone measurement: how important is the morning blood draw? Total testosterone averaged 411.7 ng/dL from 8 to 11 AM. versus 368.3 ng/dL outside this window, with lower averages later in the afternoon and evening. https://europepmc.org/article/MED/26360789
- Bremner, Vitiello and Prinz, Loss of circadian rhythm in blood testosterone levels with aging in normal men. This study found that the early morning testosterone surge seen in young men was markedly attenuated or absent in healthy older men. https://europepmc.org/article/MED/6841562
- Winters SJ (1991). Diurnal rhythm of testosterone and luteinizing hormone in hypogonadal men. Journal of andrology, 12(3), 185–190. https://pubmed.ncbi.nlm.nih.gov/1917682/
- Brambilla, DJ, Matsumoto, AM, Araujo, AB, & McKinlay, JB (2009). The effect of diurnal variation on the clinical measurement of serum testosterone and other sex hormone levels in men. The Journal of Clinical Endocrinology and Metabolism, 94(3), 907-913. https://doi.org/10.1210/jc.2008-1902
