For women, fertility begins a gradual decline around age 30 and drops more sharply after 35. For men, the decline starts later and is more gradual, but sperm quality falls meaningfully after 35 as well. The specifics matter, though, because “decline” doesn’t mean “gone.” Here’s what the numbers actually look like at each stage.
Female Fertility by Age
A woman’s peak reproductive years fall between the late teens and late 20s. During this window and into the early 30s, a healthy couple has roughly a 1 in 4 chance of conceiving in any given menstrual cycle. That probability holds fairly steady through the early 30s, then begins to erode.
The mid-30s mark a turning point. After 35, the decline accelerates noticeably. By 40, the per-cycle chance of conception drops to about 1 in 10. By 45, getting pregnant naturally is unlikely for most women.
A large North American preconception study tracked how long it actually takes couples to conceive at different ages. Among women aged 28 to 30, about 62% were pregnant within six cycles of trying, and nearly 78% within twelve. Women aged 37 to 39 saw those numbers drop to 46% at six cycles and 67% at twelve. For women 40 to 45, only about 28% conceived within six cycles, and roughly 56% within a year. The decline is real, but it’s also more gradual than many people assume. A 38-year-old still has reasonable odds with time.
Why Egg Quality Changes
The decline isn’t just about having fewer eggs, though that’s part of it. Women are born with all the eggs they’ll ever have, and that supply shrinks steadily over a lifetime. By the late 30s, the pool is significantly smaller.
The bigger issue is chromosomal quality. As eggs age, they become more likely to contain the wrong number of chromosomes, a problem called aneuploidy. Among women aged 25 to 30, roughly 25% of embryos are chromosomally abnormal. After 35, that rate climbs above 50%. By age 44, it reaches about 88%. An embryo with the wrong chromosome count typically either fails to implant, results in a miscarriage, or in rarer cases leads to a chromosomal condition like Down syndrome.
This is the main reason miscarriage rates climb with age. The risk of miscarriage is lowest in women aged 25 to 29, at about 10%. It stays relatively low through the early 30s, then rises: around 17% for women 35 to 39, 32% for women 40 to 44, and over 53% for women 45 and older.
Measuring Ovarian Reserve
If you’re wondering where you stand, doctors can measure a hormone called AMH (anti-Müllerian hormone) through a simple blood test. AMH reflects the size of your remaining egg supply. It doesn’t tell you about egg quality, but it gives a useful snapshot of how many eggs you have left relative to other women your age.
AMH levels naturally drop over time. Typical ranges fall from roughly 10 to 56 pmol/L in women aged 20 to 25, down to about 1 to 41 pmol/L in women 41 to 45, and plummet to 0.14 to 5 pmol/L after 46. A low AMH for your age group can signal diminished ovarian reserve, which may mean fewer eggs are available for conception or retrieval during fertility treatment. Your doctor can interpret your specific number in context.
Male Fertility Declines Too
Men don’t face the same hard biological clock, but the idea that male fertility is unaffected by age is a myth. Sperm quality starts shifting around 30, and the drop becomes significant after 35. In one study of over 1,200 men, sperm count, motility (the ability of sperm to swim effectively), and the percentage of normally shaped sperm all fell meaningfully in men over 35. Motility, for example, dropped from an average of about 48% in men under 35 to 33% in men aged 43 to 49. Sperm volume also declined, from around 2.8 mL in younger men to 1.7 mL in men over 50.
Sperm motility decreases by roughly 0.8% per year, which translates to a 12% to 16% reduction over two decades. That’s a slower trajectory than the female decline, but it adds up. After 40, men face higher rates of subfertility and increased risk of adverse pregnancy outcomes with their partners, including miscarriage. Research shows that DNA damage in sperm accumulates with age, which contributes to these problems.
Paternal Age and Offspring Health
Advanced paternal age carries risks that go beyond conception difficulty. Children of older fathers have a modestly increased risk of several health conditions. Fathers over 35 show about a 25% excess risk of childhood brain cancers in their offspring. Fathers 45 and older face a threefold increase in the risk of retinoblastoma, a rare eye cancer. There are also associations with cleft lip and palate, independent of the mother’s age.
Some complex conditions show a link as well. Schizophrenia risk increases with paternal age, and several autosomal dominant genetic conditions (like achondroplasia, the most common form of dwarfism) become more likely because older sperm carry more new genetic mutations. The absolute risk of any single condition remains small, but the pattern across multiple outcomes is consistent: older paternal age introduces more genetic variability, and not always in a benign direction.
What the Timeline Looks Like in Practice
Fertility doesn’t fall off a cliff at any single birthday. For women, the practical picture looks something like this: in your 20s and early 30s, conception odds are at their highest and miscarriage risk at its lowest. From about 32 to 37, fertility fades gradually enough that most couples still conceive within a year of trying, but it may take a few extra months compared to a couple in their mid-20s. After 37, the decline picks up speed. Each year matters a bit more, and by 40 to 42, the combination of fewer eggs, more chromosomal errors, and higher miscarriage rates means a significant share of couples will need fertility assistance.
For men, the timeline is stretched out. Quality starts slipping after 30, becomes more noticeable after 35, and is clearly impaired after 45. Unlike women, men continue producing new sperm throughout life, so the decline is never absolute. But “still producing sperm” and “optimal fertility” are very different things.
One practical takeaway: when a couple is struggling to conceive and the male partner is over 35, his age is worth evaluating alongside hers. A semen analysis can reveal whether sperm count, motility, or morphology have declined enough to be contributing to the problem.