Fertility and Age: What the Numbers Say for Both Partners

Maybe you are wondering whether there is still time, or you have been trying for a few months and nothing has happened yet. Most couples in which the woman is under 40 conceive within a year, but with age that share falls and the wait gets longer: more steeply for women, less steeply but noticeably for men. If pregnancy does not come, both partners are assessed, and from about 35 nobody is asked to wait a full year.

When to see a doctor

Right away — 999 in the UK, 911 in the US, 112 in the EU:

you might be pregnant (a late period is enough, even with a negative test) and you have sudden, sharp, intense tummy pain, feel very dizzy or faint, sick or look very pale. This can be a ruptured ectopic pregnancy, which needs urgent surgery (NHS);
severe or worsening pelvic pain, sudden intense pain low in the tummy with dizziness or a very high temperature — possible pelvic inflammatory disease or another emergency (NHS);
for a man: sudden, severe pain in a testicle, or testicle pain lasting more than an hour — possible torsion, which needs urgent treatment (NHS).

The same day — 111 or your GP in the UK, urgent care or your doctor in the US:

you might be pregnant, even without a positive test, and have pain low down on one side, vaginal bleeding or a brown watery discharge, or pain in the tip of the shoulder. Bleeding from an ectopic pregnancy is easy to mistake for a period (NHS);
pelvic pain that comes and goes or pain deep inside during sex — possible pelvic inflammatory disease, which can damage fertility; especially urgent if you might be pregnant (NHS).

Book an appointment:

a year of regular sex without contraception and no pregnancy: in the UK, NICE (NG257) offers assessment to both partners;
sooner with age: in the US, ASRM advises assessment after 6 months from about 35 and straight away after 40; in the UK, NICE refers to a specialist at the first appointment if the woman is 36 or over;
straight away at any age if a cause is known or suspected: absent or very irregular periods, endometriosis, previous pelvic surgery or chemotherapy, a known problem in either partner (NICE NG257).

What is happening

The overall picture. In the UK, NICE NG257 (2026) tells couples that over 80% conceive within a year if the woman is under 40 and they have regular sex without contraception; of those who do not, about half conceive in the second year, over 90% in total. The breakdown by the woman's age below comes from a 2004 European study with sex twice a week (Dunson et al., reproduced in NG257):

Woman's age	Pregnant within 1 year	Within 2 years
19–26	92%	98%
27–29	87%	95%
30–34	86%	94%
35–39	82%	90%

Two things follow. The decline is gradual, with no cliff on a birthday. And these are averages for a population, not your personal forecast. There are no rows for 40 and over because that study had too few data, not because the chance is zero.

Why it falls in women. The main reason is eggs: their number and their quality. ACOG (US, Committee Statement 22, 2025) gives rough figures: 1–2 million egg cells at birth, 300,000–500,000 at puberty, about 25,000 at 37 and about 1,000 at 51, the average age of menopause in the US. There is no standard test of egg quality. ACOG also notes that people overestimate their chances of pregnancy at every age, and what IVF can do.

Men age too. NICE says male fertility falls with age "to a lesser extent". The American urology and reproductive medicine societies (AUA/ASRM) describe modest declines in semen volume, motility and the share of normally shaped sperm, while damage to sperm DNA (fragmentation) increases with age. When the father is 40 or older, some problems in the child are somewhat more common; this is an association, not proven cause and effect. In about half of couples with infertility a male factor is the whole or part of the cause (AUA/ASRM), which is why both are tested together.

What a blood test does not tell you. The anti-Müllerian hormone (AMH) test is often sold as a "fertility clock". NICE advises against using it to predict natural conception: it only helps predict how the ovaries respond to stimulation in IVF.

IVF does not cancel age. In the UK in 2024 (HFEA, provisional data, own eggs), births per embryo transferred were 38% at ages 18–34 and 8% at 43–44, with an average of 30%. NICE (UK) offers NHS-funded IVF with a limit by age: up to three full cycles, with up to three more considered, before 40, and one cycle at 40–41 for those who have not had IVF before.

What to do

Sex every 2–3 days through the cycle gives the best chance (NICE); there is no need to plan it around ovulation.
Both partners: stopping smoking helps (smoking lowers fertility in women and is linked to poorer semen); a BMI of 30 or more makes conception take longer for women and lowers fertility in men (NICE). For men, drinking within the UK limit of 14 units a week, spread out, is unlikely to affect sperm; for a woman trying to conceive, not drinking is safest — see alcohol: an honest look. A consistent link between caffeine and infertility has not been shown, and tight underwear has not been shown to matter.
Tell the doctor about every medicine, including testosterone, anabolic steroids, finasteride, weight-loss injections (GLP-1 drugs) and cannabis (NICE).
Folic acid before conception: supplements without testing.
Go together. A semen analysis is a simple test; if it is abnormal, NICE repeats it, ideally three months later, because sperm take about that long to form.
Keep a cycle diary — what a normal cycle is — and write down questions: bring questions to the doctor.
Not ready yet: methods compared in contraception effectiveness by method.

When this is not the case

A miscarriage or ectopic pregnancy during that year does not restart the count: NICE (UK) keeps the original timeline.
Insemination (same-sex couples, single parents): in the UK, NICE offers assessment after six cycles of insemination.
Cycles that change around 40: see perimenopause starts earlier than most people expect; changes before 40 deserve a doctor's look.
Complementary therapies for infertility have not been properly evaluated (NICE).

Sources

Checked: 24 September 2026