How Accurate Is Mid-Parental Height for Predicting a Boy's Adult Height?

By The Growth Path Editorial Team · Reviewed September 2026

The mid-parental height formula is the standard first-pass estimate pediatric endocrinologists use. It is meaningfully accurate as a midpoint, but the honest confidence range is wide.

The formula

MPH midpoint (cm) = (Mother's height + Father's height + 13) / 2

Confidence band is usually ± 8.5 cm; some sources use ± 10 cm.

How accurate is the midpoint?

• 60-70% of adult heights fall within ± 8.5 cm of the midpoint.
• ~90% fall within ± 15 cm.
• Tends to underpredict in tall families, overpredict in short families (regression to the mean).

Why the range is that wide

1. Regression to family mean. Adult height regresses toward the average of all ancestors.
2. Puberty timing. Delayed puberty tends toward the higher end. Early puberty often falls short of midpoint.
3. Environment. Nutrition, illness, and sleep shift outcomes 1-3 inches.

How pediatricians use the number

• Tracking well inside the range = normal.
• Tracking below the low end = worth investigating.
• Tracking well above midpoint = usually tall genetics or early puberty.

The formula's blind spots

• Adopted or donor-conceived children require biological history.
• Estimated parent heights are only as accurate as the estimate.
• Grandparent heights are not used but matter.
• Chronic illness, GH deficiency, thyroid issues, celiac can pull actual height below predicted.

Alternative formulas

• Tanner formula: Same midpoint, wider ± 10 cm.
• Khamis-Roche: Uses current height, weight, and mid-parental height.
• Bone-age based: Gold standard, requires wrist x-ray.

What to do with the range

1. Calculate the midpoint and range.
2. Track his percentile against CDC data.
3. If percentile is well below the range low end AND dropping, bring both to the pediatrician.

Height data uses the CDC 2000 Growth Charts for boys. This page is parent education, not medical advice or diagnosis. If you have concerns about your son's growth, talk to his pediatrician, ideally with 6-12 months of measurements in hand. © 2026 The Growth Path.