How to Predict Your Child's Adult Height (And How Accurate It Is)

If your toddler is already the tallest in their class — or the shortest — it’s natural to wonder where they’ll land as an adult. Scientists have a formula for this, and while it’s not crystal-ball accurate, it gives a surprisingly useful estimate based on something you already know: how tall each parent is. The timeline for reaching that adult height differs by sex — when do girls stop growing covers the female plateau, and when do boys stop growing covers the male timeline.

The Mid-Parental Height Formula

The most widely used method for predicting a child's adult height is the mid-parental height formula — sometimes called the target height or genetic potential height formula. It averages both biological parents' heights and adjusts for the child's sex.

Formula:

For a boy: Predicted height = (Father's height + Mother's height) ÷ 2 + 6.5 cm

For a girl: Predicted height = (Father's height + Mother's height) ÷ 2 − 6.5 cm

Or in inches:

• Boys: (Father's height + Mother's height) ÷ 2 + 2.5 in
• Girls: (Father's height + Mother's height) ÷ 2 − 2.5 in

The result provides the target midpoint, with a range of ±5 cm (±2 inches) covering roughly two thirds of children, and ±10 cm (±4 inches) covering about 95%.

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Worked Examples

Source: Tanner JM et al. The Lancet, 1970; mid-parental height formula

How a Child's Current Height Relates to Their Predicted Target

For children between ages 2 and the onset of puberty, their height percentile typically tracks within approximately 1–2 standard deviations of their mid-parental target. If a child's current height percentile is well below what the mid-parental formula would predict, it's worth discussing the gap with a pediatrician.

This is exactly what the GrowthKit child height prediction calculator does — it takes both parents' heights and your child's current measurements to show predicted adult height plotted against the growth curve.

What Else Influences Adult Height?

Genetics explains 60–80% of height variation between people in well-nourished populations. The remaining 20–40% comes from:

Source: WHO Multicentre Growth Reference Study; Lango Allen H et al. Nature, 2010

Height Velocity: The Better Growth Signal

While final height is what parents often think about, height velocity — the rate of growth — is what pediatricians track most closely year to year. Understanding what typical infant height looks like in the early months gives you a useful baseline — see our guide to normal baby height growth and the baby length-for-age chart for WHO reference data.

A child who is consistently at the 20th percentile but growing at a normal rate is growing normally. A child who suddenly drops height velocity — for example, growing less than 5 cm (2 inches) per year between ages 3 and puberty — warrants investigation regardless of their current percentile.

When to Ask About Growth

Reasons to discuss height with your pediatrician include:

• Child's height is below the 3rd percentile and mid-parental target is significantly higher
• Height has dropped across 2 or more major percentile channels
• Height velocity appears to have slowed (less than 4–5 cm/year between ages 3 and puberty)
• Child's height percentile is significantly lower than weight percentile for the same age (asymmetric growth)
• Signs of early puberty in girls under 8 or boys under 9 (may compress final height)

Most healthy children of short-statured parents are simply following their genetic target. A single below-average reading in a well child without concerning symptoms rarely indicates a problem. The trend over time is the story.