Child Height Prediction Calculator
The Three Prediction Methods Explained
1. Mid-Parental Height (MPH)
The most widely used and simplest method, recommended by the American Academy of Pediatrics and used routinely in pediatric clinics. It estimates a child's genetic height potential from parental heights alone.
MPH = (Father's height + Mother's height + 13) ÷ 2For girls:
MPH = (Father's height + Mother's height − 13) ÷ 2Heights in cm. The 13 cm constant reflects the average male-female height difference. Predicted range: MPH ± 10 cm covers ~95% of children with those parental heights.
2. Khamis-Roche Method
The most accurate non-radiological method for children aged 4–17, published in Pediatrics in 1994. It incorporates the child's current age, height, weight, and both parental heights into a regression model, reducing prediction error to approximately ±2.1 inches (5.3 cm) for boys and ±1.7 inches (4.2 cm) for girls — significantly more precise than MPH alone.
Adult height = a₀ + a₁(child ht) + a₂(child wt) + a₃(midparent ht)Girls:
Adult height = b₀ + b₁(child ht) + b₂(child wt) + b₃(midparent ht)Regression coefficients differ by age group (2-year bands). All values in inches for original formula; this calculator converts to cm internally.
3. Double-at-Two Rule
A simple folk heuristic with reasonable population-level accuracy: a child's height at age 2 is approximately half their adult height. More precise versions apply a small sex adjustment — boys' adult height is approximately 2× height at 2; girls' adult height is approximately 2× height at 2 minus 2.5 cm, reflecting the earlier female growth plateau.
Adult height ≈ Height at age 2 × 2Girls:
Adult height ≈ Height at age 2 × 2 − 2.5 cmAccuracy: ±8–10 cm. Best used as a quick cross-check, not a primary prediction. Most reliable for children with heights near the median at age 2.
Which method should you use? If you have the child's current measurements and both parents' heights, the Khamis-Roche method gives the most accurate prediction. If you only have parental heights, use Mid-Parental Height. If you have a pediatric measurement from around age 2, use Double-at-Two as a cross-check. All three methods give statistical estimates — not guarantees.
Method Accuracy Comparison
| Method | Inputs Required | Error (Boys) | Error (Girls) | Best Age |
|---|---|---|---|---|
| Mid-Parental Height | Parent heights only | ±5 cm | ±5 cm | Any |
| Khamis-Roche | Age + ht + wt + parents | ±5.3 cm | ±4.2 cm | 4–17 yrs |
| Double-at-Two | Height at age 2 | ±8–10 cm | ±8–10 cm | Age 2 only |
| Bone Age (Greulich-Pyle) | X-ray required | ±2–3 cm | ±2–3 cm | Any |
Bone age assessment using hand X-ray is the most accurate non-genetic method and is performed by pediatric endocrinologists when precise height prediction is clinically important.
Factors That Affect Adult Height Beyond Genetics
Mid-parental height and other formula-based methods predict the genetic ceiling — the height a child would reach under ideal conditions. Several modifiable and non-modifiable factors influence whether a child achieves that ceiling.
Frequently Asked Questions
How accurate is the mid-parental height formula?
The mid-parental height formula predicts adult height with an error of approximately ±5 cm (±2 inches) for about 68% of children — meaning about two-thirds of children will fall within 5 cm of the prediction. For 95% of children, the actual adult height falls within ±10 cm of the predicted value. The formula is most accurate when both parents' heights are measured accurately (self-reported heights tend to be slightly inflated, which introduces systematic error into the prediction).
Can I improve my child's predicted adult height?
The mid-parental height prediction represents the genetic ceiling — the height achievable under ideal conditions. You cannot exceed this ceiling through lifestyle changes, but many children fall short of it due to nutritional deficits, inadequate sleep, chronic illness, or extreme physical stress. Ensuring adequate protein, calcium, vitamin D, and zinc intake; consistent sleep of appropriate duration; and routine pediatric monitoring are the highest-leverage interventions for helping a child reach their genetic potential.
At what age do children stop growing?
Growth plate closure typically occurs by age 16–18 in girls and 18–21 in boys, though timing varies with individual pubertal development. Girls usually reach adult height 2–3 years after their first menstrual period. Boys continue to grow modestly until their early twenties in many cases, though the majority of height gain is complete by age 17–18. Children with constitutional growth delay may grow until slightly later than typical.
Why might my child be shorter or taller than predicted?
Height prediction formulas estimate the most probable outcome based on available inputs, but they cannot capture individual variation in pubertal timing, growth plate sensitivity to hormones, genetic variation beyond midparent height (including grandparental heights and other relatives), or the cumulative effect of nutritional and environmental factors across the entire growth period. A child who is significantly shorter than predicted consistently deserves a pediatric evaluation — not because the formula is correct and the child is wrong, but because understanding why can reveal modifiable factors or treatable conditions.
Is the Khamis-Roche method better than mid-parental height?
For children aged 4–17 where current measurements are available, yes — the Khamis-Roche method reduces prediction error by roughly 20–30% compared to mid-parental height alone. It does this by incorporating the child's current height trajectory and weight into the regression model, which captures both the genetic potential and how well the child is currently tracking toward it. However, the difference in absolute terms is modest — roughly 1–2 cm of additional precision — so for most practical purposes both methods are useful and complementary.
