Age and fertility: how pregnancy chances change with age

Female fertility begins to decline around 30 and falls faster from the mid-30s

The American College of Obstetricians and Gynecologists (ACOG) describes a woman's peak reproductive years as the late teens to the late 20s. Fertility starts to decline by about 30, the decline speeds up in the mid-30s, and by 45 a natural pregnancy is unlikely (ACOG, 2023). ACOG's guide to evaluating infertility places the faster decline after age 37 (ACOG, 2020, reviewed 2026). The practice committee of the American Society for Reproductive Medicine (ASRM) puts relative fertility at 40 at about half that of women in their late 20s and early 30s (ASRM, 2022).

Published estimates of the chance per cycle differ in size

Sources agree on the direction of the change and differ on how large it is:

• 20s and early 30s: around 1 in 4 (ACOG, 2023), or 25 to 30 in 100 (ACOG, 2020, reviewed 2026; ASRM patient fact sheet, revised 2023).
• Age 30: about 20 in 100 for a healthy, fertile woman (ASRM patient booklet, 2012).
• Age 40: around 1 in 10 (ACOG, 2023), less than 10 in 100 (ACOG, 2020, reviewed 2026), 10 in 100 or less (ASRM fact sheet, "Defining infertility", 2023), and fewer than 5 in 100 (ASRM booklet, 2012).

These are patient-education figures that do not all rest on the same studies, and the oldest of them, the 2012 ASRM booklet, gives the lowest. Taken together, they put the chance at 40 at between about 1 in 20 and 1 in 10 per cycle. The guide to the chances of getting pregnant covers the figures for the whole population.

Over a full year, most women under 40 still conceive

The yearly figures change less with age than the per-cycle figures, because each cycle is another chance. In data from Dunson and colleagues (2004), reproduced in the UK's national fertility guideline (National Institute for Health and Care Excellence, NICE, 2026), the share of women pregnant when trying with intercourse twice a week was:

• aged 19 to 26: 92 in 100 after 1 year, 98 in 100 after 2 years
• aged 27 to 29: 87 in 100 after 1 year, 95 in 100 after 2 years
• aged 30 to 34: 86 in 100 after 1 year, 94 in 100 after 2 years
• aged 35 to 39: 82 in 100 after 1 year, 90 in 100 after 2 years

The table stops at 39. NICE's general statement, that more than 80 in 100 couples conceive within a year, applies only when the woman is under 40 (NICE, 2026).

The decline comes mainly from the number and quality of eggs

A woman is born with all the eggs she will have. Their number falls with age, and a larger share of those that remain have abnormal chromosomes (ACOG, 2023). StatPearls, a peer-reviewed clinical reference, reports that the rate of aneuploidy, meaning an abnormal number of chromosomes, rises from about 20 in 100 to about 60 in 100 by age 40 (StatPearls, 2026). Conditions that can affect fertility, such as uterine fibroids and endometriosis, also become more common with age (ACOG, 2023).

ASRM points to the high success rate of pregnancy with eggs donated by younger women as evidence that egg quality is the main barrier to pregnancy at older ages (ASRM booklet, 2012).

Tests of ovarian reserve do not predict natural conception

Blood tests and ultrasound measures of ovarian reserve estimate the remaining supply of eggs. ASRM states that none of them has been proven to predict reliably whether a woman will become pregnant, although they can show that age-related changes in the ovaries have begun (ASRM booklet, 2012).

Men's fertility also declines with age, less predictably

ACOG notes that a man's fertility declines with age, though not as predictably as a woman's (ACOG, 2023). ASRM's current patient fact sheet places the change later than in women, with changes in sperm in the mid-to-late 40s that can affect fertility and can cause genetic and developmental problems in children (ASRM, "Does my age affect my fertility?", 2023). Its earlier booklet placed the point at which sperm quality generally becomes a problem in a man's 60s (ASRM booklet, 2012).

Age shortens the recommended wait before an evaluation

US guidance recommends an evaluation after 12 months of trying under 35, after 6 months from 35, and before trying over 40 (ASRM, "Definition of infertility", 2023; ACOG, 2023). UK guidance uses 36 rather than 35, and from that age recommends referral to a specialist at the first appointment (NICE, 2026). The guide on when to see a doctor about fertility sets out both.