Estimate your child's likely adult height based on both parents' heights.
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The mid-parental height method estimates a child's likely adult height by averaging both parents' heights, then adding roughly 6.5cm for a boy or subtracting roughly 6.5cm for a girl (a simplified version of the classic "add or subtract 13cm and divide by two" formula), since males are, on average, taller than females due to the effects of testosterone during puberty on growth plates. This method, sometimes called the Tanner method after auxologist James Tanner who helped popularize it clinically, is a widely used pediatric estimate, though genetics is far more complex than two numbers averaged together — height is influenced by dozens of genes with small individual effects, not a single dominant one. Actual adult height typically falls within about 8–10cm of this estimate in either direction, and childhood nutrition, chronic illness, and overall health during growing years can meaningfully shift a child's actual adult height away from the genetically predicted midpoint, sometimes substantially in cases of significant nutritional deficiency or medical conditions affecting growth.
Parents are naturally curious how tall their child will grow up to be, and the mid-parental height method offers the simplest available estimate — averaging both parents' heights and adjusting for the average height difference between men and women. It requires no medical testing, just two numbers most parents already know, which is exactly why it remains a popular starting point despite being far from precise.
The method traces back to auxology, the study of human growth, and versions of it have been used clinically for decades as a quick pediatric reference point. The adjustment for sex — roughly 6.5cm added for a boy or subtracted for a girl from the parental average — reflects the well-documented average height difference between adult men and women, driven substantially by testosterone's effect on growth plates during male puberty.
Height is genetically complex in a way this simple formula can't fully capture. Large genetic studies have identified hundreds of gene variants that each contribute a small amount to height, rather than a single gene or even a handful of genes determining the outcome, which is part of why predictions built on just two data points carry real uncertainty — typically plus or minus 8 to 10 centimeters even when parental heights are known precisely.
Environmental factors add another layer of unpredictability. Adequate childhood nutrition, absence of chronic illness, and general health during the growing years all matter for whether a child reaches their genetically influenced height potential; significant malnutrition or certain medical conditions during childhood can measurably suppress final adult height below what parental heights alone would predict.
For a more individualized and accurate prediction later in childhood, pediatricians can use bone age X-rays combined with a child's own growth curve tracked over time, which becomes a considerably stronger predictor than parental height alone as a child gets older and their own growth pattern becomes established. The mid-parental estimate remains most useful as an early, rough approximation rather than a precise forecast.
It's a reasonable population-level estimate, generally accurate within about 8cm, but individual genetics and childhood health can shift actual results.
This reflects the average height difference between adult men and women, which the formula accounts for when averaging both parents' heights.
The mid-parental method gives a rough lifelong estimate from birth, but pediatricians typically get more accurate individual predictions later in childhood using bone age X-rays and growth curve tracking, since a child's own growth pattern becomes a stronger predictor than parental height alone as they get older.