Height is a polygenic trait, which means that many genes work together to shape it, and studies suggest that about 60% to 70% of differences in height between people are decided by the heights of their parents. Children in a family often grow in similar patterns, although each child grows at their own pace. Kids cannot change the genes that decide how tall they will be, but healthy eating habits and being active help them make the most of it.

The growth spurt from baby to toddler adds roughly half of a child's adult height, and in the first year a baby grows about 10 inches longer on average. From about age 2, kids usually grow about 2 and a half inches taller each year, and kids tend to grow a bit faster in the spring than in other seasons. Nobody grows at a perfectly steady rate. When researchers measured infants' length weekly, twice weekly or daily during their first 21 months, they found that growth came in bursts of 0.5 to 2.5 centimeters, separated by stretches of 2 to 63 days with no measurable growth. Slowing down is built into mammal growth, because growth is rapid in early life and then slows, and this slowdown comes from strong suppression of cell division in many tissues, driven mainly by local rather than body-wide mechanisms.

Long bones are the bones that are longer than they are wide, and a long bone does not grow from its middle outward, because it grows at each end, next to a growth plate. Growth plates are the places where children's bones make new bone, so the bones can grow longer. Inside a growth plate, cartilage cells multiply and grow in length, and then they change into hard, mineralized bone. The growth plate helps decide the future length and shape of the grown-up bone. A growth plate is weaker than solid bone, so it is easier to injure. When a person is fully grown, the growth plates harden into solid bone, and after a growth plate has closed, that bone is no longer growing longer.

A bone age X-ray is a picture of the hand and wrist. In the standard method, doctors take an X-ray of the non-dominant hand and wrist and compare the bones with an atlas of reference pictures. The first atlas of hand bones appeared soon after X-rays were discovered in 1895, and in 1898 John Poland published one showing the hand and wrist bones of 19 British children aged 1 to 17 years. The two best-known bone age methods date from 1959 and 1962. The most accurate way doctors guess adult height uses a child's current height together with a bone age X-ray of the hand and wrist.

Height is controlled by many genes, each with a modest effect, and as of November 2026 scientists have found more than 700 such gene variants. Some of them are in genes that affect cartilage in growth plates, and a growth plate is made of cartilage, a rubbery, flexible material, but the roles of many height genes are still unknown. Kids cannot change the genes that decide how tall they will be, and eating well supports growth, but eating extra food or extra vitamins does not make a child grow taller.

Doubling a child's height at age 2 is a popular rule of thumb for guessing adult height, but no research shows it is accurate. The mid-parental method for guessing adult height can be off by about 4 inches up or down. Careful measuring takes a standard routine, because children's movements and where they look affect the reading, and standardized protocols would help to reduce this error. The most accurate way doctors guess adult height uses a child's current height together with a bone age X-ray of the hand and wrist.

Words to know

• polygenic: from many genes
• cartilage: rubbery tissue
• atlas: picture book
• variants: gene versions