A female baby is born with roughly 1 to 2 million eggs in her ovaries. That sounds like an enormous number, but it’s already a steep decline from the peak: during fetal development, around the 20th week of gestation, egg count reaches approximately 6 to 7 million. From that point forward, the number only goes down. No new eggs are ever created after birth.
Why the Count Drops Before Birth
Egg cells begin forming early in fetal development, multiplying rapidly until they hit that peak of 6 to 7 million around mid-pregnancy. Then a natural process called follicular atresia kicks in. Immature follicles (the tiny sacs that each contain one egg) stop developing, break down, and get reabsorbed by the body. This isn’t a sign that something has gone wrong. It’s a built-in quality control system, and it operates continuously from before birth through menopause.
By the time a baby girl is born, atresia has already eliminated roughly two-thirds to more than four-fifths of her original egg supply, leaving those 1 to 2 million. The process continues through childhood. By age 7, only about 300,000 primordial follicles remain, even though the ovaries haven’t started cycling yet.
How Many Eggs Remain at Puberty
By the time a girl gets her first period, her ovaries hold approximately 300,000 to 400,000 eggs. That’s a fraction of what she started with, but still far more than she will ever use. Of those hundreds of thousands, only about 400 will fully mature and be released during ovulation across her entire reproductive life. The rest, well over 99%, will be lost to atresia.
Each menstrual cycle, a group of follicles begins to develop, but typically only one “wins” and releases an egg. The rest of the group degenerates. This means the ovaries lose eggs at a much faster rate than the one-per-month rhythm of ovulation might suggest. Hundreds of follicles can be lost in a single cycle.
Egg Count by Age
The decline isn’t perfectly steady. It accelerates as you get older, with the sharpest drop happening in the late 30s. Here are the general averages:
- Birth: 1 to 2 million eggs
- Puberty: 300,000 to 400,000 eggs
- Age 40: approximately 25,000 eggs
- Menopause: fewer than 1,000 eggs
These are averages, and individual variation is significant. Two women the same age can have very different egg reserves. Genetics plays a large role, as does smoking, certain medical treatments, and ovarian surgery. The timeline isn’t identical for everyone, which is why some women experience earlier fertility decline than others.
Egg Quantity vs. Egg Quality
The raw number of eggs tells only part of the story. Egg quality, meaning how likely an egg is to result in a healthy pregnancy, also declines with age. Eggs are more prone to chromosomal errors as you get older, which is why miscarriage rates and the chance of certain genetic conditions increase in the late 30s and 40s. A 40-year-old with 25,000 remaining eggs doesn’t have the same fertility outlook as a 25-year-old with the same count, because the eggs themselves have aged.
This distinction matters practically. Fertility treatments can sometimes work around low egg quantity by stimulating the ovaries to mature more follicles in a single cycle. But they can’t reverse age-related changes in egg quality.
How Egg Reserve Is Measured
If you’re curious about your own egg supply, doctors can estimate it using a blood test that measures anti-Mullerian hormone (AMH). This hormone is produced by the small follicles in your ovaries, so higher levels generally indicate a larger remaining reserve. Typical AMH values decline predictably with age:
- Age 25: around 3.0 ng/mL
- Age 30: around 2.5 ng/mL
- Age 35: around 1.5 ng/mL
- Age 40: around 1.0 ng/mL
- Age 45: around 0.5 ng/mL
Levels below 1.0 ng/mL are considered low, and levels below 0.4 ng/mL are severely low. An ultrasound counting the visible follicles on your ovaries (called an antral follicle count) is often used alongside AMH for a more complete picture. Neither test can assess egg quality directly, but together they give a reasonable estimate of how many eggs you have left.
What Happens at Menopause
Menopause occurs when the egg supply drops to roughly 1,000 or fewer. At that point, the ovaries can no longer sustain regular hormone cycling, periods stop, and natural conception is no longer possible. The average age of menopause is 51, but it can happen anywhere from the early 40s to the late 50s. The underlying trigger is the same: the reserve has been depleted below the threshold needed to keep the reproductive system running.
The entire arc, from 7 million eggs at mid-gestation to fewer than 1,000 at menopause, spans decades but follows a single unbroken pattern of decline. Understanding where you fall on that curve can be useful context if you’re thinking about family planning, considering egg freezing, or simply trying to make sense of your fertility.