Age does affect sperm quality, though the decline is more gradual than the sharp fertility drop women experience. Starting in a man’s late 30s to early 40s, measurable changes appear in semen volume, sperm motility, DNA integrity, and the shape of sperm cells. These changes accumulate over time, with the most pronounced effects typically showing up after age 45.
What Changes in Sperm After 40
When researchers compared 30-year-old men to 50-year-old men, they found declines across nearly every measure of semen quality: semen volume dropped by 3 to 22%, sperm motility fell by 3 to 37%, and the percentage of normally shaped sperm decreased by 4 to 18%. Sperm concentration (the raw number of sperm per milliliter) appears to hold relatively steady with age, which means older men still produce plenty of sperm. The problem is that more of those sperm move poorly or carry structural abnormalities.
The decline in semen volume becomes especially noticeable past 45. Men between ages 45 and 48 produce an average of about 2.8 mL per ejaculate, while men older than 56 average closer to 1.95 mL. For reference, the World Health Organization considers anything above 1.3 to 1.5 mL to be within normal range, so most older men still fall within that window. But a smaller volume combined with slower, less well-formed sperm does add up.
DNA Damage Increases With Age
Beyond the visible characteristics of sperm, there’s a subtler and arguably more important change: the integrity of the DNA inside each sperm cell. A study of over 2,100 semen samples found that sperm DNA fragmentation worsened significantly with age. Men 35 and younger had an average DNA fragmentation rate of 14.7%, compared to 15.9% for men aged 36 to 44, and 16.2% for men 45 and older.
Those numbers may look close together, but they represent a real statistical trend, and DNA fragmentation matters because it affects what happens after fertilization. Damaged DNA can lead to failed implantation, early miscarriage, or, in some cases, health conditions in the child. The damage appears to be linked to deteriorating mitochondrial function inside sperm cells, meaning the tiny energy-producing structures that power sperm movement are also involved in protecting genetic material, and both decline together.
Why Sperm Quality Drops
The testes are vulnerable to a process called oxidative stress, where reactive molecules accumulate and damage cells faster than the body can repair them. In younger men, antioxidant defenses in testicular tissue keep this process in check. As men age, those defenses weaken. Animal studies show that the production of both enzymatic and non-enzymatic antioxidants drops with age, allowing oxidative damage to build up in the cells that produce sperm.
This leads to visible changes at the tissue level: degenerative changes in testicular tissue, the appearance of small fluid-filled pockets (vacuoles) in sperm-producing cells, and an overall reduction in the number of those cells. The result is sperm that are produced more slowly, move less effectively, and carry more genetic errors. Unlike women, who are born with a fixed supply of eggs, men continuously produce new sperm throughout life. But the cellular machinery doing that production becomes less reliable over time.
Risks for Pregnancy and Miscarriage
Paternal age doesn’t just affect whether conception happens. It also influences whether a pregnancy succeeds. In a study of egg donation cycles (which controls for the mother’s age by using eggs from younger donors), the miscarriage rate was 23.8% when the father was over 45, compared to 16.3% when he was 45 or younger. After adjusting for other variables, men over 45 had a 61% higher odds of miscarriage. This is significant because the use of donor eggs removes maternal age as a factor, isolating the father’s contribution.
The American Society for Reproductive Medicine acknowledged in a 2025 ethics opinion that advancing paternal age, described as a continuum beginning in a man’s 40s and 50s, is associated with increased risk of stillbirth, pregnancy complications, and a buildup of new genetic mutations in sperm. Notably, there’s no agreed-upon cutoff age the way there is for “advanced maternal age” at 35. The absence of a clear threshold has led many men to assume their age doesn’t matter for reproduction, which the evidence contradicts.
Effects on Children’s Health
Older fathers pass along more spontaneous genetic mutations with each year. Sperm from a 40-year-old carries roughly twice as many new mutations as sperm from a 20-year-old, because every cycle of sperm cell division is another opportunity for copying errors to slip in. Some of these mutations are harmless. Others are not.
A 10-year increase in paternal age is associated with a 21% higher risk of autism spectrum disorder in offspring. Children of fathers younger than 20 or older than 45 had a 1.72-fold increased risk of developing poor social skills compared to children of fathers aged 25 to 29. Research from translational studies also links advanced paternal age to elevated rates of schizophrenia-spectrum traits. These are population-level statistics, meaning the absolute risk for any individual child remains low, but the relative increase is consistent across multiple large studies.
What This Means for IVF and Fertility Treatment
Paternal age can also affect the success of assisted reproduction, though the picture depends on the specific technique used. In standard IVF cycles where the female partner was 35 to 39 years old, live birth rates dropped from 27% when the male partner was under 35 to just 18.8% when he was over 50. That’s a meaningful decline of nearly a third.
Interestingly, this effect disappeared when a technique called ICSI was used, in which a single sperm is injected directly into the egg. ICSI bypasses many of the barriers that aging sperm struggle with, such as penetrating the egg’s outer layer. In couples where the woman was under 35 or over 40, male age had less impact on live birth rates regardless of technique, likely because younger women compensate for lower sperm quality while older women face their own dominant fertility limitations.
These findings suggest that for couples where the man is over 40 and the woman is in her late 30s, the choice of fertilization method during IVF could meaningfully affect their chances. It also reinforces that male age is not irrelevant in fertility planning, even when assisted reproduction is on the table.
The Practical Timeline
Sperm quality doesn’t fall off a cliff at any single age. The decline is gradual, starting with subtle changes in a man’s mid-to-late 30s and becoming more measurable after 40. The most clinically significant effects, including higher miscarriage rates, reduced IVF success, and increased genetic mutation rates, cluster around age 45 and beyond. Men in their 40s can and do father healthy children regularly, but the odds shift with each passing year in ways that are now well documented. For men considering starting or expanding a family later in life, a semen analysis provides a straightforward snapshot of where things stand.