How tall will my child be?
The single best predictor of a child's adult height is the parents' heights. About 80% of adult height variation is genetic, and most of that genetic signal comes through both biological parents in roughly equal share. The remaining 20% comes from environmental factors — nutrition (especially in the first 3 years and during puberty), sleep, chronic illness, hormonal balance.
The Height Predictor uses the mid-parental height method (also called the Tanner formula), the standard pediatric estimate:
For boys: predicted height = (father's + mother's) / 2 + 6.5 cm (~2.5 in)
For girls: predicted height = (father's + mother's) / 2 − 6.5 cm (~2.5 in)
The 6.5 cm adjustment reflects the average height difference between adult men and women (~13 cm). Adding/subtracting half that adjustment converts the sex-neutral parental midpoint to a sex-specific prediction.
How to use the calculator
- Pick your preferred units — feet/inches or centimetres.
- Pick the child's biological sex. The formula adjusts based on the average male/female adult height difference.
- Enter both parents' heights. The calculator accepts feet/inches in formats like 5'10" or 5'10, or just inches like 70, or centimetres directly.
- The predicted adult height appears immediately, plus a 95% confidence range (roughly ±8.5 cm or ±3.4 in).
Worked examples
Example 1 — Average parents, son
Father 5'10" (178 cm), Mother 5'5" (165 cm).
- Mid-parental average: 171.5 cm.
- Add 6.5 cm for son: 178 cm ≈ 5'10".
- 95% range: ~169.5–186.5 cm (5'7" to 6'1.5").
Example 2 — Same parents, daughter
Mid-parental average: 171.5 cm.
- Subtract 6.5 cm for daughter: 165 cm ≈ 5'5".
- 95% range: ~156.5–173.5 cm (5'2" to 5'8.5").
Example 3 — Tall parents, son
Father 6'2" (188 cm), Mother 5'10" (178 cm).
- Mid-parental: 183 cm.
- Add 6.5 cm: 189.5 cm ≈ 6'2.5".
- 95% range: ~181–198 cm (5'11" to 6'6").
Example 4 — Mixed parents, daughter
Father 6'4" (193 cm), Mother 5'0" (152 cm).
- Mid-parental: 172.5 cm.
- Subtract 6.5 cm for daughter: 166 cm ≈ 5'5.5".
- 95% range: ~157.5–174.5 cm (5'2" to 5'9").
- Note: when parents have very different heights, real outcomes have more spread than the formula's standard range suggests.
What "95% confidence range" means
About 95% of children whose parents fit the inputs will have an adult height within the range shown. About 5% will fall outside it — some shorter, some taller. The point estimate is the most likely single value; the range is a more honest picture of the uncertainty.
Why such a wide range? Because the genetic-environmental mix is complex. The same parents can produce children of significantly different heights (you've probably seen this in families with multiple kids). The mid-parental estimate captures the central tendency, not the individual variation.
Why genetics aren't 100%
Even though height is highly heritable, it's not deterministic. Several environmental factors can move the needle by inches:
Nutrition
Sustained malnutrition (especially in the first 1000 days of life and during puberty) reduces final height — sometimes by inches. Average adult height in many populations has risen significantly over the past century, mostly due to better childhood nutrition. Dutch men are now ~13 cm taller than they were 150 years ago, despite the gene pool being relatively stable.
Sleep and growth hormone
Growth hormone is released primarily during deep sleep, especially in the first sleep cycle. Chronically sleep-deprived kids may not reach their genetic potential. The standard recommendation: 9-12 hours for school-age kids, 8-10 for teens.
Chronic illness
Conditions like celiac disease (untreated), severe asthma, chronic kidney disease, growth hormone deficiency, or hypothyroidism can suppress growth. Diagnosis and treatment in childhood often allow significant catch-up growth.
Stress and emotional environment
Severe early stress (psychosocial dwarfism is a recognized condition) can suppress growth. Adequate caregiving environment matters more for very young children than is sometimes appreciated.
Hormonal status
Early puberty can reduce final height (puberty closes growth plates). Late puberty often allows more growth. Both extremes are sometimes worth investigating with a pediatric endocrinologist.
The mid-parental method's limitations
It's a population average
The 6.5 cm sex adjustment is the average across many populations. Individual ethnic groups have slightly different male-female height differences (some larger, some smaller), and the formula doesn't capture this nuance.
It assumes equal contribution
Both parents contribute equally on average, but in any given family, one parent's genes may dominate. You've probably noticed kids who clearly take after one side.
It doesn't capture extreme cases
For parents at the extremes of height (very short or very tall), real outcomes regress slightly toward population means. A 6'8" father and 5'0" mother won't necessarily produce a 5'10" son — the son might be closer to 5'8" because both parents are statistical outliers and children tend toward the middle.
It can't account for unique medical issues
If a child has a growth disorder, a chronic illness, or significant nutritional gaps, the prediction overstates their likely adult height.
More accurate methods (when available)
Bone age (X-ray)
A pediatric endocrinologist can X-ray a child's wrist and compare growth-plate fusion to standard reference ages. The "bone age" plus current height plus several known formulas gives a much more precise prediction. This is the gold standard for kids who are already growing actively.
Growth-curve tracking
Plot the child's height on a CDC or WHO growth chart over years. Children typically track along a percentile ("75th percentile") consistently. If they're solidly on the 50th percentile at age 2 and still on the 50th at age 8, their adult height should land near the 50th percentile (about 5'9" for US males, 5'4" for US females). Deviation from a stable percentile is a flag for medical evaluation.
Multiple regression formulas
Researchers have built more elaborate predictive models incorporating current height, weight, age, and parental data. These tend to be more accurate but require more inputs and are mostly used in clinical settings.
What to do with the prediction
Use it as a sanity check
If your kid is on track to hit the predicted range, things are normal. Most kids are. Don't worry about being a few inches above or below the prediction — that's well within the 95% range.
Don't treat it as destiny
Predictions are estimates. A short prediction doesn't doom your kid; a tall prediction doesn't guarantee a basketball career. Real outcomes depend on factors the formula can't capture.
Talk to a pediatrician if growth seems off
Concerning patterns: dropping multiple percentiles between visits, growing very slowly compared to peers, growing extremely fast (could indicate early puberty), being well outside the parental prediction range. Most of the time these turn out to be normal variation, but some warrant medical evaluation.
Focus on what matters more
Adult height is mostly fixed at birth (genetically). Things that ARE actionable for your kid's life outcomes: sleep habits, nutrition, exercise, social and emotional development, education, sense of self-worth. Many of these matter far more than the inch or two of height that environmental factors can swing.
Common questions and concerns
"What if I don't know one of the parents' heights?"
Use a population average for the missing parent's sex (US average: ~5'9" for men, ~5'4" for women) and treat the result as more uncertain. The 95% range will be wider than the formula suggests.
"Can supplements or growth hormone make my kid taller?"
For kids with diagnosed growth hormone deficiency, treatment with synthetic growth hormone is medically established and adds inches. For kids with normal growth hormone levels, growth hormone treatment doesn't change adult height — there's no shortcut. Specific supplements (calcium, vitamin D) are important for bone health but don't add height beyond genetic potential.
"Why are kids today taller than their grandparents?"
Mostly nutrition. Average adult heights in developed countries have risen 5-10 cm over the past century as childhood nutrition improved. The trend has plateaued in places where nutrition is now near-optimal. In countries still emerging from poverty, the trend is still rising.
"Will my child be taller than me?"
Statistically often yes, especially in places where nutrition has improved generation over generation. But individual outcomes vary — about half the kids whose parents had access to good nutrition end up about as tall as the same-sex parent, and about half differ in either direction.
What the calculator gives you, summarized
- Predicted adult height — using the mid-parental (Tanner) formula, sex-adjusted.
- 95% confidence range — ±8.5 cm (±3.4 in), the standard statistical range for the formula.
- Unit flexibility — feet/inches or centimetres for input and output.
- Forgiving input parsing — accepts 5'10", 5'10, 70 (inches), or 178 (cm).
- Honest framing — the calculator is upfront that ~5% of kids fall outside the range, and that significant deviations from the prediction warrant medical evaluation.
Two parents in, an adult-height range out. The standard pediatric estimate, with all its inherent uncertainty acknowledged.