Men don’t hit a single age where fertility switches off. Unlike menopause, which ends female fertility within a relatively narrow window, male reproductive decline is a slow, continuous process with no hard cutoff. The testes keep producing sperm throughout life, but sperm quality, quantity, and the ability to achieve pregnancy all worsen progressively starting in the late 30s and accelerating through the 40s and 50s.
That said, “not infertile” and “fully fertile” are very different things. A man at 55 may still be capable of fathering a child, but the odds are meaningfully lower, it will likely take longer, and the risks to a pregnancy are higher than they were in his 20s.
How Sperm Quality Changes With Age
The clearest evidence of male reproductive decline shows up in semen analysis. A study comparing men under 35 to men over 45 found that older men had significantly lower sperm motility, the measurement of how well sperm swim toward an egg. Progressive motility dropped from about 39% in the younger group to 28% in the older group. Semen volume also fell, from 3.2 mL to 2.5 mL. Interestingly, sperm shape (morphology) didn’t differ meaningfully between the two groups, suggesting that motility and volume are the parameters most sensitive to aging.
Beyond what’s visible under a microscope, the DNA inside sperm also deteriorates. A sperm DNA fragmentation index, or DFI, measures how much genetic damage sperm carry. Over 25% of semen samples from men older than 45 have a DFI above 30%, a threshold associated with higher failure rates in fertility treatments and a greater need for IVF. Younger men are far less likely to cross that line.
The Hormonal Side of the Equation
Testosterone levels decline gradually as men age. This doesn’t stop sperm production entirely, but it slows it. The testes continue making sperm, just at a reduced rate, and the fluid that carries sperm contains fewer living cells. Lower testosterone can also reduce sex drive and make sexual responses slower and less intense, which indirectly affects the likelihood of conception even when sperm are still being produced.
How Long It Takes to Conceive
One of the most practical ways to understand male fertility decline is how long it takes a couple to get pregnant. Among men under 25, about 77% impregnated their partners within six months. For men over 45, that number dropped to roughly 53%. Women with male partners aged 45 or older were almost five times more likely to take over a year to conceive compared to those with partners under 25.
These numbers assume the female partner’s age is also a factor, but even after accounting for maternal age, the pattern holds. Older fathers independently make conception slower and less certain.
Risks During Pregnancy and for Offspring
Getting pregnant is only part of the picture. The father’s age also affects what happens after conception. A national survey analysis found that pregnancies fathered by men aged 50 or older had roughly twice the odds of ending in miscarriage compared to those fathered by men aged 25 to 29, even after adjusting for the mother’s age and other factors. For early miscarriages (within the first 12 weeks), the risk was even slightly higher, at about 2.3 times the odds.
The American Society for Reproductive Medicine notes that advancing paternal age, a continuum beginning in a man’s 40s and 50s, is linked to increased risk of stillbirth, pregnancy complications, and a buildup of new genetic mutations in sperm. These mutations can lead to rare single-gene disorders and may contribute to conditions like autism and schizophrenia in offspring. Each year a man ages, his sperm cells have gone through more rounds of division, and each division is an opportunity for copying errors in DNA.
Does IVF Overcome the Age Problem?
Fertility treatments can help, but the picture is nuanced. A large study of over 56,000 frozen embryo transfer cycles found that when the female partner was under 36, the father’s age didn’t significantly reduce the chance of a live birth. Men aged 45 and older had comparable pregnancy rates, miscarriage rates, and live birth rates to younger men in these IVF cycles.
This sounds reassuring, but it comes with important context. IVF labs can select the best-looking sperm and embryos, which filters out some of the damage that would matter in natural conception. The study also didn’t capture the subtler genetic risks that might not show up until a child is older. And IVF success still depends heavily on the egg quality of the female partner, which means the male age effect may be partially masked when younger eggs are used.
The 40s and 50s Are the Key Decades
There’s no medical consensus on a single age that defines “too old” for fatherhood. The American Society for Reproductive Medicine acknowledged in its 2025 guidance that no agreed-upon cutoff exists for advanced reproductive age in men. What the evidence does show is a clear pattern: fertility starts declining in a man’s late 30s, becomes noticeably impaired through the 40s, and carries meaningful pregnancy risks by the 50s.
If you’re a man in your 40s or older thinking about having children, the most useful thing to know is that you’re likely still fertile, but “fertile” covers a wide range. Conception may take significantly longer, the odds per cycle are lower, and the risks to a pregnancy are real. A semen analysis, including DNA fragmentation testing, can give you a concrete picture of where you stand rather than relying on age alone. Men who know they want children later in life also have the option of freezing sperm at a younger age, preserving the quality of those cells before the gradual decline takes hold.