How to Predict Your Child's Adult Height

The most common way to estimate how tall a child will grow is the mid-parental method: average the two parents' heights, then adjust up or down depending on whether the child is a boy or a girl. It's the formula pediatricians reach for first, and it gets you a reasonable ballpark in seconds. The height predictor runs it for you — but it's worth understanding what it's doing, and, just as importantly, how rough the answer really is. This is an estimate, not a medical assessment.

The mid-parental formula

Start by adding both biological parents' heights and dividing by two to get the mid-parental height. Then adjust:

• For a boy: add 2.5 inches (about 6.5 cm) to the average.
• For a girl: subtract 2.5 inches (about 6.5 cm) from the average.

The adjustment reflects the fact that adult men are, on average, about 5 inches taller than adult women — so you split that difference around the parents' midpoint.

A worked example

Say the father is 5'11" (71 in) and the mother is 5'5" (65 in):

• Average: (71 + 65) ÷ 2 = 68 inches
• For a son: 68 + 2.5 = 70.5 inches, about 5'10½"
• For a daughter: 68 − 2.5 = 65.5 inches, about 5'5½"

That's the central estimate. Real children land in a range around it, which is the part people tend to forget.

How accurate is it?

Honestly? It's a guide, not a guarantee. The mid-parental estimate typically lands within about 4 inches (10 cm) either way of a child's actual adult height — a spread of nearly 8 inches from top to bottom. Genetics account for roughly 80% of height, but the rest — nutrition, sleep, general health, and timing of puberty — moves the needle, and none of it is captured by a formula built on two numbers. Treat the result as a reasonable middle, not a target.

Other ways height gets predicted

• The "double it at age 2" rule. A rough shortcut: double a child's height at age 2 (girls sometimes measured at 18 months) for a very loose adult estimate.
• Growth percentile tracking. Pediatricians plot height on a growth chart over time; a child who tracks steadily along the 50th percentile tends to stay near it.
• Bone-age X-ray. The most accurate method is clinical — an X-ray of the hand estimates skeletal maturity and remaining growth. That's a doctor's tool, not a home one.

What the estimate can't tell you

A formula can't diagnose anything. If you're worried a child is growing much faster or slower than expected, or falling off their percentile curve, that's a conversation for a pediatrician — not a calculator. Used in the right spirit, though, it's a fun and harmless way to picture the future. To work out a child's exact current age for percentile tracking, the age calculator helps, and the BMI calculator covers the weight-for-height side once they're grown.

Frequently asked questions

How do I predict my child's adult height?

Average both biological parents' heights, then add 2.5 inches for a boy or subtract 2.5 inches for a girl. That mid-parental figure is the standard first estimate.

How accurate is the mid-parental height method?

It usually lands within about 4 inches (10 cm) of the child's eventual adult height. It's a reasonable middle estimate, not a precise prediction, because nutrition, health, and puberty timing also matter.

Can you really tell how tall a child will be?

Not exactly. You can estimate a likely range. Genetics drive roughly 80% of height, so parents' heights give a solid ballpark, but no formula accounts for everything that shapes growth.

What is the "double height at age 2" rule?

A rough shortcut that doubles a child's height at age 2 to estimate adult height. It's far less reliable than the mid-parental method and should be treated as a fun guess.

Does the formula work the same for boys and girls?

The average of the parents' heights is the same; the adjustment differs. You add 2.5 inches for boys and subtract 2.5 inches for girls, reflecting the average height difference between adult men and women.