The numbers, age by age
Your egg supply peaks before you are born, at around six to seven million about halfway through pregnancy. By birth it is one to two million. By puberty roughly 300,000 to 500,000 remain. At 37 the average is about 25,000, and at 51, the average age of menopause in the United States, about 1,000.
Another way to see it is as a share of what you started with. A widely cited model of ovarian reserve puts the average at about 12% remaining by age 30 and about 3% by 40. These are averages across many women. Two healthy women of the same age can have very different numbers.
See the curve for your own age
Where do they all go?
Only a few hundred eggs, roughly 400 to 500, are ever released through ovulation in a lifetime. The rest are lost through a natural process called atresia. It continues every month whether or not you ovulate, are pregnant, or use birth control.
Nothing you did caused it, and nothing known today stops it.
Count is only half the story
As eggs age, a larger share of them carry chromosomal errors. That makes pregnancy harder to achieve and miscarriage more likely, and it is why age is such a strong factor in fertility. According to the American College of Obstetricians and Gynecologists, fertility declines gradually from around 32 and more quickly after 37.
It also means a number on a lab report cannot tell you whether you will be able to conceive. Women with a low count conceive, and women with a high count can still need help.
How to find out your own
No test counts every egg. Two tests estimate your reserve: a blood test for anti-Müllerian hormone (AMH), and an ultrasound that counts the small follicles visible in your ovaries. Together they show whether your supply is high, typical or low for your age.
That is useful for planning, especially if you are thinking about freezing eggs, because it helps predict how many eggs one cycle is likely to collect.
What ovarian reserve tests can and can’t tell you