Most girls reach their final adult height between ages 14 and 16, while most boys stop growing between ages 16 and 18. But these are averages, and the real answer depends on when puberty starts, how long it lasts, and a handful of factors your child can actually influence.
Girls: Growth Slows After the First Period
For girls, the pubertal growth spurt kicks off around age 9 on average. They hit their fastest rate of growth at about age 11.5, gaining roughly 8 centimeters (just over 3 inches) per year at peak speed. After that, growth gradually tapers off.
The most useful milestone for predicting when a girl will stop growing is her first period. The average height gain after that point is about 7 centimeters (3 inches), but the timing of the period matters a lot. Girls who get their period at age 10 tend to grow another 10 centimeters (4 inches) afterward, while those who don’t start until age 15 typically gain only about 5 centimeters (2 inches). This is why girls who enter puberty early don’t necessarily end up shorter than their peers. They grow for a longer stretch before their period arrives, then continue growing for a longer stretch afterward.
The growth plates in a girl’s bones, the cartilage zones near the ends of long bones where lengthening happens, begin fusing around ages 16 to 17. By age 20 to 21, complete fusion is seen in virtually all females.
Boys: A Later Start and a Bigger Spurt
Boys begin their growth spurt about two years later than girls, with the “takeoff” happening around age 11. Peak growth velocity lands at roughly age 13.5, when boys gain an average of 9.5 centimeters (close to 4 inches) per year. That’s faster than the female peak, and the total height gained during puberty is larger too: about 30 to 31 centimeters (12 inches), compared to 27.5 to 29 centimeters (11 inches) in girls. This pubertal contribution accounts for roughly 17 to 18 percent of a boy’s final adult height.
Growth plate fusion in boys starts later than in girls, typically by about two years. Initial signs of complete fusion at the knee appear around ages 17 to 18, and 100 percent of males show full fusion by ages 21 to 22. Most boys are functionally done growing in height by 18 or so, though a small amount of growth can continue into the early twenties.
How Growth Plates Work
Every long bone in a child’s body has growth plates at each end. These are bands of cartilage that produce new bone tissue, gradually lengthening the skeleton. During puberty, rising levels of sex hormones both accelerate growth and, eventually, signal these plates to harden into solid bone. Once a growth plate fuses completely, that bone can no longer get longer.
Different bones close on different schedules. The forearm bones tend to fuse earlier than the knee bones, and upper limb bones show more variation in timing than lower limb bones. Doctors can estimate how much growth remains by taking an X-ray of the hand or pelvis and comparing bone maturity to standardized charts. A practical rule: once a child has reached the late stages of puberty, the growth plates are essentially closed.
Predicting Your Child’s Adult Height
Pediatricians still use a formula developed nearly 50 years ago by the researcher J.M. Tanner. It works by averaging the parents’ heights and then adjusting for the child’s sex. For a boy, you add the mother’s and father’s heights, then add 13 centimeters (about 5 inches), and divide by two. For a girl, you add both parents’ heights, subtract 13 centimeters, and divide by two. The result is called the “target height,” and most children end up within about 10 centimeters of it.
This formula gives a reasonable estimate, not a guarantee. Nutrition, sleep, chronic illness, and the timing of puberty all shift the outcome.
What Affects How Tall a Child Gets
Sleep
Growth hormone is released in pulses throughout the day, but the biggest surge happens during deep sleep, particularly in the first stretch of slow-wave sleep shortly after falling asleep. This is the phase that matters most for growth, muscle development, and tissue repair. Children and teens who consistently get insufficient sleep may blunt that nightly hormone spike. The practical takeaway: protecting sleep duration and quality during puberty directly supports the biological machinery of growth.
Nutrition
Bones need raw materials. Children and teens ages 9 to 18 need about 1,300 milligrams of calcium per day, roughly the amount in four glasses of milk or the equivalent from yogurt, cheese, or fortified foods. They also need 600 IU of vitamin D daily, which helps the body absorb that calcium. Adequate protein matters too, since bone growth requires both mineral and protein components.
On a population level, better nutrition is one reason puberty is starting earlier than it used to. Data from large surveys in China show the average age of a girl’s first period dropped from 12.33 years in 2000 to 12.00 years in 2019. Higher BMI is significantly associated with earlier puberty onset, a trend observed across many countries.
Genetics
Parental height is still the single strongest predictor. But genetics also influence the tempo of growth, meaning when puberty starts and how quickly it progresses. Some families consistently produce “late bloomers” who enter puberty later but ultimately reach a normal adult height.
Late Bloomers vs. Growth Disorders
Constitutional delay of growth and puberty is the medical term for a child who simply develops on a slower timeline. These kids are often shorter than classmates during middle school, enter puberty a year or two later than average, and then catch up. It runs in families. If a parent was a late bloomer, there’s a good chance their child will be too.
The key reassurance is that late bloomers reach a normal adult height once puberty finally runs its course. This is by far the most common reason a teenager seems “behind” in growth. It is different from conditions where the body doesn’t produce enough growth hormone or sex hormones, which require medical evaluation. If a child shows no signs of puberty by age 14 (for boys) or age 13 (for girls), or if growth has stalled completely for a year or more, a doctor can use bone age X-rays and blood tests to sort out whether it’s simply a slow timeline or something that needs treatment.