Getting pregnant takes longer than most people expect. Even under ideal conditions, a healthy couple in their 20s has only about a 25% chance of conceiving in any given month. That means the odds are actually against you each cycle, and several months of trying before a positive test is completely normal. Understanding what affects those odds can help you figure out whether something specific is working against you or whether you just need more time.
How Long It Actually Takes
The monthly probability of conception drops steadily with age. At 30, a healthy woman has roughly a 20% chance per cycle. At 35, that falls to about 15%, and by 40, it’s around 5%. These numbers mean that even without any fertility problems, it can take six months to a year of well-timed intercourse before pregnancy occurs. Many couples assume something is wrong after two or three months, when statistically they’re still well within the normal range.
Fertility specialists generally recommend a workup after 12 months of trying if you’re under 35, and after 6 months if you’re 35 or older. If you’re over 40, seeking evaluation sooner is reasonable. And if you have known risk factors like irregular periods, a history of pelvic infections, or endometriosis, testing should start right away regardless of how long you’ve been trying.
Timing Matters More Than You Think
You can only get pregnant during about six days of each menstrual cycle, a stretch called the fertile window. This window includes the five days before ovulation and the day of ovulation itself. The highest-probability days are the two to three days just before you ovulate, because sperm can survive in the reproductive tract for up to five days while an egg only lives about 12 to 24 hours after release.
If you’re having sex regularly (every two to three days throughout the month), you’re likely hitting the window without needing to track anything. But if your cycles are irregular or you’re not having frequent intercourse, it’s easy to miss it entirely. Ovulation predictor kits, basal body temperature tracking, and cervical mucus monitoring can all help you identify when you’re most fertile.
Ovulation Problems
The most common reason women struggle to conceive is irregular or absent ovulation. Polycystic ovary syndrome (PCOS) is one of the leading causes. In PCOS, the ovaries produce higher-than-normal levels of androgens (sometimes called “male hormones,” though all women produce them). These elevated hormones interfere with egg development, so eggs either aren’t released on schedule or aren’t released at all. If your periods are unpredictable, very far apart, or absent, this is one of the first things worth investigating.
A less obvious issue is a short luteal phase. The luteal phase is the stretch between ovulation and your next period. A normal luteal phase runs 12 to 14 days, giving a fertilized egg enough time to travel to the uterus and implant. If yours is shorter than 10 days, the uterine lining may shed before an embryo has a chance to establish itself. You can estimate your luteal phase by tracking ovulation and counting the days until your period starts.
Structural and Tissue-Related Causes
Even if you’re ovulating normally, physical barriers can prevent sperm and egg from meeting. Blocked or damaged fallopian tubes are a significant cause of infertility. The most common culprit is scarring from past pelvic infections, particularly untreated chlamydia or gonorrhea, which can cause pelvic inflammatory disease. Many women don’t realize they ever had these infections because they can be asymptomatic. Prior abdominal or pelvic surgery can also cause adhesions that affect the tubes.
Endometriosis is another common factor. This condition occurs when tissue similar to the uterine lining grows outside the uterus, often on the ovaries, fallopian tubes, or pelvic walls. It can cause infertility through several routes: scar tissue and adhesions can physically block egg release or transport, the fluid environment inside the pelvis can become hostile to sperm and eggs, and chemical changes in the uterine lining itself can make it harder for an embryo to implant. Endometriosis doesn’t always cause severe pain, so some women don’t know they have it until they start investigating fertility issues.
It’s Not Always a Female Factor
Roughly half of all infertility cases involve a male factor, either alone or in combination with a female factor. Despite this, many couples initially focus testing entirely on the woman. A semen analysis is one of the simplest and least invasive fertility tests available, and it should be among the first steps in any evaluation.
The test measures several things: sperm concentration (the lower reference limit is 15 million per milliliter), motility (at least 40% of sperm should be moving), and morphology (at least 4% should have a normal shape). Values below these thresholds don’t mean pregnancy is impossible, but they do reduce the odds per cycle. Low sperm counts, poor motility, and abnormal morphology can result from varicoceles (enlarged veins in the scrotum), hormonal imbalances, heat exposure, certain medications, smoking, heavy alcohol use, or genetic factors. In some cases the cause is never identified.
Egg Quality and Age
Age affects fertility not just by reducing egg quantity but by changing egg quality. As women get older, a higher percentage of their eggs carry chromosomal abnormalities (aneuploidy), which prevent normal embryo development or lead to early miscarriage. The rate of aneuploidy rises predictably after the mid-20s. Among women 26 to 37, the chance of having no chromosomally normal embryos in a given cycle is quite low, around 2% to 6%. By age 42, that figure climbs to 33%, and by 44, it reaches 53%.
This is the main reason fertility declines so sharply in the late 30s and 40s. You may still be ovulating regularly and have no structural problems, but if a high percentage of eggs are chromosomally abnormal, most fertilized embryos won’t develop or won’t implant. This process is invisible from the outside. Your cycle can look perfectly normal while the underlying egg quality has shifted significantly.
Unexplained Infertility
After a full workup, about 22% to 28% of couples receive a diagnosis of unexplained infertility. This doesn’t mean nothing is wrong. It means current testing hasn’t identified a specific cause. Standard evaluations check for ovulation, tubal patency, uterine abnormalities, and semen quality, but they can’t assess every variable involved in conception, like subtle egg quality issues, sperm function beyond what a basic analysis captures, or the complex molecular interactions required for implantation.
Unexplained infertility is somewhat more common in women over 35 (about 26%) compared to those under 35 (about 21%), which likely reflects the growing role of egg quality as a hidden factor. For couples with this diagnosis, treatment typically progresses through options like ovulation-stimulating medications combined with timed intercourse, then intrauterine insemination, and eventually IVF if needed. Many couples with unexplained infertility do conceive, sometimes with treatment and sometimes on their own with additional time.
Lifestyle Factors That Shift the Odds
While lifestyle changes alone won’t overcome a structural blockage or severe sperm abnormality, they can meaningfully affect conception chances at the margins. Being significantly over or underweight disrupts hormonal signaling and can interfere with ovulation. Smoking damages eggs and sperm, reduces sperm count, and accelerates the age-related decline in egg quality. Heavy alcohol consumption is associated with reduced fertility in both partners.
Chronic stress, sleep deprivation, and excessive exercise can all suppress the hormonal signals that drive ovulation. For men, heat exposure matters: frequent hot tub use, laptop use on the lap, and prolonged sitting can raise scrotal temperature enough to temporarily impair sperm production. These factors are worth addressing not because they’re guaranteed to be the reason you haven’t conceived, but because they’re the variables within your control while you sort out whether a bigger issue exists.