You can get pregnant as soon as you start ovulating, which typically happens shortly before or after your first period. For most girls, that means pregnancy is biologically possible between ages 10 and 14, with the average age of a first period now sitting at about 11.9 years for those born after 2000. Fertility then continues until menopause, which occurs around age 51 on average. The window between those two points spans roughly four decades, but your chances of conceiving shift dramatically from one end to the other.
When Pregnancy First Becomes Possible
Pregnancy requires ovulation, the release of an egg from the ovaries. This process usually begins around the time of a girl’s first menstrual period, known as menarche. A Harvard study tracking generational trends found that the average age of menarche has dropped from 12.5 years for those born in the 1950s and 1960s to 11.9 years for those born between 2000 and 2005. About 15.5% of girls in that younger group started their periods before age 11, and roughly 1.4% started before age 9.
What makes this tricky is that ovulation can occur before a girl ever has a visible period. The first egg release happens in advance of the first bleed, so pregnancy is technically possible even before any outward sign of puberty-related menstruation appears. This is uncommon, but it’s the reason doctors emphasize that fertility begins with ovulation, not with a period.
Peak Fertility: Your 20s and Early 30s
Fertility is highest in the late teens through the late 20s. During this window, a healthy person who is trying to conceive has roughly a 20 to 25% chance of becoming pregnant in any given menstrual cycle. That per-cycle probability holds fairly steady into the early 30s before it begins to slide.
The reason for this peak comes down to egg quality and quantity. Girls are born with about 2 million eggs. By puberty, that number has already dropped to around 400,000. Throughout the reproductive years, eggs are lost each month, not just the one that’s released during ovulation but hundreds of others that naturally break down. In your 20s, the remaining eggs are more likely to be chromosomally normal, which means they’re more likely to result in a healthy pregnancy and less likely to end in miscarriage. The risk of miscarriage for women aged 25 to 29 is about 10%.
How Fertility Changes After 35
The American College of Obstetricians and Gynecologists defines “advanced maternal age” as 35 or older at the time of delivery. This threshold was chosen because both fertility rates and the risk of chromosomal abnormalities shift noticeably around this point, though ACOG itself acknowledges it’s somewhat arbitrary. Some risks don’t meaningfully increase until 40 or later.
By age 37, around 25,000 eggs remain. That sounds like plenty, but most of those eggs are no longer viable for a healthy pregnancy. The per-cycle chance of conceiving drops to roughly 10 to 15% by the mid-30s and continues falling. Miscarriage rates climb as well, largely because older eggs are more likely to have chromosomal errors that prevent normal development.
None of this means pregnancy after 35 is unlikely or dangerous. Millions of people conceive and carry healthy pregnancies in their late 30s and beyond. But the statistical shift is real: it takes longer to conceive on average, and the odds of complications rise with each passing year.
Fertility After 40
After 40, the decline accelerates. The monthly chance of conceiving drops to around 5% or less per cycle without assisted reproduction. Miscarriage risk climbs steeply: by age 45 and older, more than half of all recognized pregnancies end in miscarriage, according to a large registry-based study published in The BMJ. The underlying cause is the same, a higher proportion of eggs with chromosomal abnormalities.
Pregnancies that do continue past the first trimester at these ages carry elevated risks of gestational diabetes, high blood pressure, preterm birth, and the need for cesarean delivery. Genetic screening becomes particularly relevant, as the likelihood of conditions linked to extra or missing chromosomes rises significantly.
The Upper Limit: Perimenopause and Beyond
Perimenopause, the transitional phase leading to menopause, typically begins in a person’s 40s and lasts several years. During this time, periods become irregular and hormone levels fluctuate, but ovulation still occurs sporadically. The Cleveland Clinic puts it simply: as long as you’re still getting a period, even an irregular one, you should assume you’re still ovulating and can get pregnant.
Menopause is defined as 12 consecutive months without a menstrual period. At that point, the ovaries have essentially stopped releasing eggs, and natural pregnancy is no longer possible. The average age of menopause is around 51, but it can happen anywhere from the early 40s to the late 50s. The oldest verified natural conception on record belongs to Dawn Brooke of Guernsey, who conceived at age 59 in 1997.
By menopause, roughly 1,000 immature eggs remain in the ovaries, but they no longer respond to the hormonal signals that trigger ovulation. This is the biological endpoint of fertility. Assisted reproductive technologies like egg donation and IVF can extend the possibility of pregnancy beyond natural menopause, but those pregnancies rely on donor eggs rather than a person’s own.
Fertility at Every Age: A Quick Overview
- Under 15: Pregnancy is possible once ovulation begins, which can happen before a first period. Egg supply is at its highest, but the body is still developing physically.
- 20 to 29: Peak fertility. Roughly 20 to 25% chance of conceiving per cycle. Lowest miscarriage risk, around 10%.
- 30 to 34: Fertility remains strong but begins a gradual decline. Per-cycle odds dip slightly.
- 35 to 39: Noticeable drop in per-cycle conception rates. Egg reserve falls to around 25,000 by 37. Miscarriage and chromosomal risks increase.
- 40 to 44: Per-cycle odds fall to roughly 5% or less. Miscarriage risk rises significantly.
- 45 and older: Natural conception is rare but still possible before menopause. Miscarriage exceeds 50% for recognized pregnancies.
What Affects Your Individual Timeline
The ages above are population averages. Your own fertility timeline depends on genetics, overall health, ovarian reserve, and lifestyle factors. Smoking accelerates egg loss and can move menopause earlier by one to two years. Conditions like polycystic ovary syndrome or endometriosis can affect ovulation regularity and conception odds at any age. Chemotherapy and certain surgeries can reduce or eliminate ovarian function prematurely.
If you’re curious about where you stand, a blood test measuring anti-Müllerian hormone (AMH) can give a rough estimate of your remaining egg supply. It doesn’t predict whether you’ll conceive, but it provides useful context, especially if you’re planning the timing of pregnancy. An antral follicle count via ultrasound offers similar information. Both are routinely available through a gynecologist or fertility clinic.