How accurate is the mid-parent method?

The mid-parent (Galton/Tanner) method predicts adult height within about ±2 inches (5 cm) for approximately 95% of children. It accounts for roughly 60-80% of height variation, which is the heritability of height in well-nourished populations. The remaining variation comes from nutrition, overall health, sleep, puberty timing, and random genetic recombination. It's a useful estimate, not a precise prediction.

At what age can you predict adult height?

The mid-parent method can be used at any age because it only requires parental heights. For more refined predictions, bone age X-rays (after age 7-8) can identify whether a child has more or less growing time than their chronological age suggests. Pediatric endocrinologists use bone age combined with current height to refine predictions, especially for children whose trajectory diverges meaningfully from mid-parental prediction.

Can my child grow taller than predicted?

Yes. About 2-5% of children significantly exceed mid-parent prediction due to favorable nutrition, late puberty (more growing time), random genetic recombination producing tall combinations, or genes from grandparents not expressed in parents. Conversely, some children fall short due to malnutrition during growth years, chronic illness, early puberty, or unfavorable gene combinations. Tracking growth percentile over time is more informative than the prediction.

What if my child is much shorter than expected?

If your child consistently tracks well below mid-parental prediction or drops percentiles on the CDC growth chart, consult a pediatrician. Potential causes include: constitutional growth delay (late puberty — usually resolves with normal final height), familial short stature (genetics, not a disorder), growth hormone deficiency, hypothyroidism, celiac disease, chronic illness, or nutritional deficiency. Most causes are treatable when identified, and growth hormone therapy can be effective for documented deficiency cases. Earlier evaluation = more treatment options before growth plates close.

Child Height Predictor

Q: How does the mid-parent formula work?

For boys: (Father height + Mother height + 5 inches) / 2. For girls: (Father height + Mother height − 5 inches) / 2. The 5-inch adjustment reflects the average height difference between adult men and women (~5 inches / 13 cm in most populations). The result is the predicted adult height; actual outcome typically falls within ±2 inches of this prediction.

Estimate your child's predicted adult height using the mid-parent (Galton) method. Enter both parents' heights and the child's sex to get an estimated adult height range. This method is simple and provides a reasonable estimate for most families.

Adult height is approximately 60-80% heritable — meaning genetics is the dominant predictor of how tall a child will be. The mid-parent method, originally developed by Sir Francis Galton in the late 1800s and refined since (often called the Tanner method in modern pediatrics), provides a simple framework for estimating a child's predicted adult height from the heights of biological parents.

The formula: average the parents' heights, then add 2.5 inches for a son (boys are typically taller than their mothers) or subtract 2.5 inches for a daughter (girls are typically shorter than their fathers). This produces a "mid-parental height" estimate, with a typical accuracy of ±2 inches (~5 cm) for about 95% of children. The remaining variation comes from nutrition during childhood, overall health, genetic factors beyond parental height (random recombination, expression of latent height genes), and environmental factors.

This calculator estimates adult height from biological parents' heights and the child's sex. It works at any age (only parental heights are needed). For more refined predictions in older children, pediatricians can use bone-age X-rays combined with current height to identify children whose growth trajectories are likely above or below mid-parental prediction. Important: predicted height is an estimate, not a destiny. Children sometimes exceed or fall short by 3-4 inches due to nutrition, medical conditions, late or early puberty timing, and other factors. The prediction is most useful as a screening tool ("is my child growing as expected?") rather than as a precise forecast.

Inputs

Father's Height (inches)

5'10" = 70 inches

Mother's Height (inches)

5'5" = 65 inches

Child's Sex

Results

Predicted Height

5'10"

In Inches

70.0"

In Centimeters

177.8 cm

Range

68.0-72.0"

Height Prediction Details

Detail	Value
Father's Height	5'10" (70 in)
Mother's Height	5'5" (65 in)
Child's Sex	Male
Formula	(Dad + Mom + 5") / 2
Predicted Height	5'10" (70.0 in)
Predicted Height (cm)	177.8 cm
Likely Range	5'8" to 6'0"
Range (inches)	68.0 to 72.0 in

Last updated: May 27, 2026Reviewed by the CalcMountain editorial team

Formula

Mid-parent (Tanner) height prediction: For boys: Predicted adult height = (Father height + Mother height + 5) / 2 inches = (Father height + Mother height + 13) / 2 cm For girls: Predicted adult height = (Father height + Mother height − 5) / 2 inches = (Father height + Mother height − 13) / 2 cm The ±2.5 inches adjustment reflects the average height difference between adult men and women (~5 inches / 13 cm). Prediction range (95% confidence interval): Predicted ± 2 inches (~5 cm) typically captures actual adult height for ~95% of children. Example: Father 5'10" (70"), Mother 5'5" (65"). Son predicted height: (70 + 65 + 5) / 2 = 140/2 = 70 inches = 5'10" Daughter predicted height: (70 + 65 − 5) / 2 = 130/2 = 65 inches = 5'5" Likely range for son: 5'8" to 6'0" (5'10" ± 2 inches) Likely range for daughter: 5'3" to 5'7" (5'5" ± 2 inches) Why the formula works (and its limitations): Genetics contribute ~60-80% of height variation. The mid-parent height captures the genetic average passed down. The remaining variation comes from: - Nutrition during growth years (especially protein, calcium, vitamin D, zinc) - Overall health and absence of chronic disease - Sleep (growth hormone release during deep sleep) - Puberty timing (early puberty often = shorter adult height; late puberty = often taller) - Random genetic recombination (children sometimes inherit "tall" or "short" allele combinations from grandparents) The formula assumes both biological parents are well-nourished and reached their genetic height potential. For families where a parent's growth was stunted by malnutrition or illness, the formula underestimates true genetic potential. Beyond mid-parent prediction: Pediatric endocrinologists may use: - Bone-age X-rays: skeletal maturity vs. chronological age — children with delayed bone age have more growing time remaining - Growth velocity tracking: deviation from expected curve flags potential issues - Height-for-age percentiles over time: percentile changes can indicate growth disturbance Adult height is reached around age 14-15 for girls (about 2 years after first menstruation) and 16-17 for boys (about 4 years after pubertal onset).

How to use this calculator

Enter biological father's adult height in inches (5'10" = 70").
Enter biological mother's adult height in inches (5'5" = 65").
Select the child's sex (boys typically grow ~2.5" taller than mid-parental average; girls ~2.5" shorter).
Review predicted adult height and likely range (±2 inches).
For non-biological parents (adopted, step-parents): the formula doesn't apply since it uses genetic inheritance. Use the child's biological parents' heights if known.
If a biological parent's height was reduced by malnutrition or illness during their growth years, the formula may underestimate the child's genetic potential. Use grandparents' heights as additional reference.
For more precise prediction, consult a pediatrician — bone-age X-rays after age 7-8 combined with current growth can refine estimates significantly for children whose trajectory diverges from mid-parental prediction.
Track child's height percentile over time on CDC growth charts. Consistent percentile is the healthy pattern; sudden drops or jumps warrant pediatric assessment.

Worked examples

Average-height family, son

Father 5'10" (70"), Mother 5'5" (65"). Son. Predicted: (70 + 65 + 5) / 2 = 70" = 5'10" Likely range: 5'8" to 6'0" Matches population average male height (~5'9-5'10"). Son will likely fall close to father's height. Within range encompasses about 95% of likely outcomes.

Tall parents, daughter

Father 6'2" (74"), Mother 5'9" (69"). Daughter. Predicted: (74 + 69 − 5) / 2 = 69" = 5'9" Likely range: 5'7" to 5'11" Daughter will likely be tall (above average female height of ~5'4"). Tall heritage tends to produce tall children. Note: there's a small "regression to the mean" effect where children of unusually tall parents tend to be slightly less tall than the mid-parent prediction (and children of unusually short parents tend to be slightly taller), but the effect is small relative to formula uncertainty.

Mixed-height parents, son

Father 5'6" (66"), Mother 5'9" (69"). Son. Predicted: (66 + 69 + 5) / 2 = 70" = 5'10" Likely range: 5'8" to 6'0" Son's prediction is essentially the average of parents adjusted for male offset. Notice the predicted height exceeds either parent's height — this isn't an error. Genetics combine in complex ways, and a son's predicted adult height is based on the mid-parental average plus the sex offset, which can land outside the range of either parent. Reality: actual height will depend on which specific height-influencing genes the son inherits from each parent, plus environmental factors. Result could be anywhere from ~5'7" to 6'0"+ even within "normal" inheritance.

When to use this calculator

Use this calculator out of curiosity, when planning pediatric care, when concerned about your child's growth trajectory relative to expectations, or when discussing growth concerns with your pediatrician.

The mid-parent method is the simplest and most widely used height prediction tool. For most families, it provides a useful estimate within ±2 inches.

Pair with bmi-kids (pediatric BMI tracking), ideal-weight calculator (long-term planning), and general growth tracking on CDC charts.

Important practical considerations:

1. **Genetics is dominant but not absolute.** Genetics explains 60-80% of height variation. Nutrition, health, and environment account for the rest. Children sometimes meaningfully exceed or fall short of mid-parental prediction.

2. **Track growth percentile over time.** Single height measurements matter less than the trajectory. A child consistently at the 30th percentile is fine; a child who drops from 50th to 15th percentile within a year warrants pediatric assessment.

3. **Puberty timing affects outcome.** Early puberty (especially in girls) often correlates with shorter adult height because growth plates close earlier. Late puberty often correlates with taller adult height due to extended growth window. Bone age X-rays can identify these patterns.

4. **Nutrition matters during growth windows.** Adequate protein, calcium (1000-1300 mg/day for children/teens), vitamin D, zinc, and overall calorie sufficiency support reaching genetic height potential. Restrictive diets during growth years can permanently reduce adult height.

5. **Chronic conditions affect growth.** Untreated celiac disease, growth hormone deficiency, hypothyroidism, kidney disease, and other conditions can reduce height. Children meaningfully below mid-parental prediction warrant pediatric workup.

6. **Sleep matters.** Growth hormone primarily releases during deep sleep, especially early-night cycles. Chronic sleep deprivation can reduce growth.

7. **Adoption/step-parent situations.** Mid-parent formula uses genetic inheritance. For adopted children, biological parents' heights (if known) are the relevant inputs. Step-parents and adoptive parents' heights don't predict the child's adult height genetically.

8. **Final height vs. growth velocity.** Many parents focus on the destination (final adult height). Pediatricians focus on the trajectory (consistent growth velocity, percentile maintenance). The trajectory matters more for identifying growth disorders.

9. **Regression to the mean.** Children of very tall parents tend to be slightly shorter than mid-parental prediction; children of very short parents slightly taller. This is statistical regression, not a defect — it reflects that height genes recombine and revert toward population averages over generations. Effect is small (~0.5 inches) relative to formula uncertainty.

Common mistakes to avoid

Using step-parents' or adoptive parents' heights. The formula uses genetic inheritance; only biological parents' heights apply.
Expecting precise prediction. Range is ±2 inches for 95% of children. Actual height can vary more in either direction due to environmental and genetic factors.
Ignoring growth trajectory. Single predictions matter less than tracking percentile maintenance over time on CDC growth charts.
Focusing only on final height. Pediatricians use growth velocity (rate of growth) and percentile trends to identify problems — these matter more than the prediction.
Not addressing modifiable factors. Adequate nutrition, sleep, and treatment of chronic conditions all support reaching genetic potential.
Worrying about minor variation. Children below or above the prediction by 1-2 inches are normal. Only major deviations or trajectory changes warrant pediatric assessment.

Frequently Asked Questions

Sources & further reading

Child Growth and Development — U.S. Centers for Disease Control and Prevention
Growth and Your Child — American Academy of Pediatrics
Growth Disorders — Patient Information — U.S. National Institute of Diabetes and Digestive and Kidney Diseases

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