Women are born with roughly 1 to 2 million eggs, and that number only goes down from there. Unlike sperm, which men produce continuously, a woman’s entire egg supply is set before birth. By the time a baby girl is born, she already has every egg she will ever have, and the body steadily absorbs unused eggs throughout her life.
Egg Count Before Birth and at Puberty
The peak actually happens before a girl is even born. Around 20 weeks into fetal development, a female fetus carries roughly 6 to 7 million eggs in her ovaries. From that point on, the count drops sharply through a natural process of cell death. By birth, only about 1 to 2 million remain. By the time a girl reaches puberty, the number has fallen further to somewhere between 300,000 and 500,000.
This sounds like an enormous loss, but it’s a normal part of development. The vast majority of eggs are never meant to be ovulated. They’re reabsorbed by the body in a continuous, behind-the-scenes process that runs from before birth all the way to menopause.
How Eggs Are Lost Each Month
Most people know that one egg is released during ovulation each menstrual cycle. What’s less obvious is that dozens of eggs are lost alongside it. Each month, a group of follicles (the tiny fluid-filled sacs that each contain an egg) begin developing together. One follicle becomes dominant and releases its egg at ovulation. The rest of that group simply break down and get reabsorbed. This means a woman loses roughly 15 to 20 or more eggs per cycle, not just one.
Over a reproductive lifetime spanning roughly 30 to 35 years of menstrual cycles, a woman ovulates only about 400 to 500 eggs total. The other hundreds of thousands are lost to this natural monthly attrition. That background loss is the main driver of the declining egg count, not ovulation itself.
Egg Count From Your 30s to Your 40s
The decline accelerates as women move through their 30s. By around age 37, the average woman has about 25,000 eggs remaining. According to data from the American College of Obstetricians and Gynecologists, reaching this threshold typically means menopause is about 15 years away. By age 40, most women are down to less than 10% of their pre-birth egg supply.
These are averages, and individual variation is significant. Some women lose eggs faster or slower depending on genetics, health, and environmental factors. But the overall trajectory is consistent: the decline picks up speed in the mid-to-late 30s and continues accelerating into the 40s.
Egg Quality Declines Alongside Quantity
The number of remaining eggs is only half the story. Egg quality, meaning the likelihood that an egg has the correct number of chromosomes, also drops with age. At 35, about 60% of a woman’s eggs are chromosomally normal. That percentage falls steadily after 35, which is a major reason why miscarriage rates rise and fertility treatment success rates drop for older women.
Chromosomal abnormalities in eggs happen because the cell division process that prepares an egg for fertilization becomes more error-prone over time. This is why age affects fertility even when a woman still has a reasonable number of eggs left. A 42-year-old with 10,000 remaining eggs faces lower odds per cycle than a 28-year-old, because a smaller proportion of those eggs will be viable.
What Happens at Menopause
Menopause marks the point when the egg supply is essentially exhausted. By the time a woman reaches menopause, typically around age 51, she may have fewer than 1,000 eggs remaining. At that level, the ovaries can no longer sustain regular hormone cycles, menstruation stops, and natural conception is no longer possible.
Factors That Speed Up Egg Loss
Genetics plays the biggest role in determining how quickly your egg supply declines. If your mother or sisters went through early menopause, you’re more likely to as well. But lifestyle and environmental factors also matter.
Smoking is one of the most well-documented accelerators. Research from Harvard Medical School found that chemicals in cigarette smoke can directly trigger egg cell death. This connection helps explain the longstanding link between smoking and early menopause. Women who smoke tend to reach menopause one to four years earlier than nonsmokers. Environmental pollutants that mimic the toxic chemicals in cigarettes can have a similar effect. Certain medical treatments, particularly chemotherapy and radiation to the pelvic area, can also cause rapid or permanent egg loss.
How to Estimate Your Own Egg Count
There’s no way to count eggs directly, but a blood test measuring Anti-Müllerian Hormone (AMH) gives a useful estimate of ovarian reserve. AMH is produced by the follicles in your ovaries, so higher levels generally indicate more remaining eggs. A typical AMH level falls between 1.0 and 3.0 ng/mL, while levels under 1.0 are considered low.
AMH levels decline predictably with age. According to Cleveland Clinic estimates, a 25-year-old might expect a level around 3.0 ng/mL, dropping to about 2.5 at 30, 1.5 at 35, 1.0 at 40, and 0.5 at 45. These numbers represent the lower end of typical for each age, so many women will test higher. Your doctor can also use an ultrasound to count visible follicles on the ovaries, which provides another snapshot of remaining supply.
One important caveat: AMH tells you about egg quantity, not egg quality. A high AMH at 42 means you have more eggs than average for your age, but it doesn’t change the age-related decline in chromosomal normalcy. Both numbers matter for fertility.