Child Height Predictor: Adult Height Estimate from Parent Heights Using the Mid-Parent Height Formula

The mid-parent height formula has a prediction accuracy of approximately plus or minus 4 inches at the 95% confidence level, meaning that for 95 out of 100 children with a given set of parent heights, the adult height will fall within 4 inches (above or below) of the formula’s prediction. This accuracy was established through population studies tracking children from birth to adulthood and comparing their actual adult heights to formula predictions based on parent heights. Within this range, the formula tends to be most accurate for children of parents whose heights are close to the US average (approximately 5’9″ for men, 5’4″ for women) and becomes slightly less reliable at the extremes (very tall or very short parents) because extremely unusual heights are sometimes the result of specific genetic conditions that affect growth differently than the polygenic model underlying the formula assumes. The formula also assumes that both parents’ heights are fully expressed genetic potential, meaning it is most accurate when neither parent had a childhood health condition, severe nutritional deprivation, or medical intervention (such as growth hormone treatment) that artificially altered their adult height relative to their genetic potential. In clinical practice, pediatricians use the mid-parent height calculation as one data point alongside current height percentile tracking, growth velocity (rate of growth per year), and bone age assessment to evaluate a child’s overall growth trajectory rather than relying on the formula in isolation. The American Academy of Pediatrics growth resources at aap.org and the CDC growth charts at cdc.gov together form the standard toolkit for clinical growth assessment in US pediatric practice.

Based on the most recent National Health and Nutrition Examination Survey (NHANES) data collected by the CDC, the average adult height in the United States is 5 feet 9.1 inches (175.4 cm) for non-Hispanic white men and approximately 5 feet 9 inches (175.3 cm) for all US men combined across racial and ethnic groups. For US women, the average adult height is 5 feet 4.0 inches (163 cm) for non-Hispanic white women and approximately 5 feet 3.5 inches (161.3 cm) for all US women combined. These figures are based on measured height (not self-reported) and are considered the most accurate available population estimates for US adult height. There is meaningful variation in average height across racial and ethnic groups in the US; for example, non-Hispanic Black men and women tend to be slightly taller on average than non-Hispanic white counterparts, while Asian-American and Hispanic Americans tend to have somewhat lower average heights, reflecting both genetic population differences and socioeconomic factors affecting nutrition and healthcare access during childhood that influence whether genetic height potential is fully realized. The mid-parent height formula used in this calculator implicitly assumes parent heights reflect their genetic potential, and the comparison to US average heights displayed in the results uses the combined US population average of 5’9″ for male and 5’4″ for female targets. Full NHANES height data and trend analysis is available at cdc.gov/nchs, which also tracks secular trends in US adult height over time.

The age at which children stop growing is determined by the closure of the growth plates (epiphyseal plates), the cartilaginous zones at the ends of long bones where bone elongation occurs. Growth plate closure is triggered by the hormonal changes of puberty, specifically the rising estrogen levels that accompany puberty in both sexes (testosterone is converted to estrogen in this context). For girls, the growth plates typically close approximately 2 years after the onset of menstruation, meaning girls generally reach their final adult height between ages 14 and 16, with the majority of girls completing their height by age 15. For boys, who typically enter puberty 1 to 2 years later than girls, growth plates close later, and boys typically reach their adult height between ages 16 and 18, though some boys continue growing into their early 20s at a slow rate. The timing of puberty significantly affects when growth stops; early puberty (precocious puberty) can cause the growth plates to close earlier than typical, potentially limiting adult height despite a period of rapid early growth. Delayed puberty, conversely, extends the window for growth and may allow children who are temporarily shorter during adolescence to catch up. Constitutional delay of growth and puberty (CDGP) is the most common cause of late puberty and short stature in adolescent boys in the US, and almost always resolves without treatment, with affected children reaching their full genetic height potential on a delayed timeline. CDC growth chart tracking at cdc.gov and the Pediatric Endocrine Society resources at pedsendo.org provide additional information on normal and atypical puberty timing and its effects on growth and final adult height.

For the vast majority of children growing up in the United States with adequate access to food and healthcare, the most important modifiable factors for ensuring they reach their genetic height potential (as estimated by the mid-parent formula) involve nutrition, sleep, and general health maintenance rather than any specific intervention. Adequate protein intake throughout childhood and adolescence is the most critical nutritional factor for growth, with the USDA dietary guidelines at dietaryguidelines.gov recommending increasing protein intake during the adolescent growth spurt. Calcium and vitamin D are critical for bone mineral density and growth plate function; the AAP recommends 1,000 to 1,300 mg of calcium per day for children ages 4 to 18, and most US children fall below this level. Adequate sleep is often overlooked but is critically important for growth; the majority of growth hormone (GH) secretion occurs during slow-wave (deep) sleep, and consistently inadequate sleep duration or quality can reduce GH secretion and slow growth velocity. For children who are confirmed to be growing below their predicted range and have a diagnosed medical cause, specific medical interventions exist: growth hormone therapy (synthetic GH injection) is FDA-approved and effective for children with confirmed growth hormone deficiency, Turner syndrome, chronic kidney disease, small for gestational age with failure to catch up, Prader-Willi syndrome, and idiopathic short stature (height below 2.25 standard deviations below mean without an identified cause). Growth hormone therapy is a clinical decision made by a pediatric endocrinologist based on detailed evaluation; it is not appropriate for all short children and is carefully supervised to ensure appropriate growth response and safety monitoring. The Pediatric Endocrine Society at pedsendo.org provides patient-family resources on growth hormone therapy indications, effectiveness, and safety profile for US families considering or currently pursuing this treatment for their child.

The mid-parent height formula requires both biological parent heights as inputs, because the formula’s accuracy depends on using the heights of the individuals who provided the child’s genetic material for height determination. For adopted children where one or both biological parent heights are unknown, the formula cannot be applied with the same accuracy as for children with known biological parent heights. In these cases, several practical approaches can be used: if only one biological parent height is known, some practitioners estimate the unknown parent’s height using the population average for that sex (5’9″ for a biological father, 5’4″ for a biological mother) and apply the formula with this substituted value, understanding that the result carries additional uncertainty beyond the usual plus or minus 4 inches. If both biological parent heights are unknown (fully anonymous adoption), the formula is not applicable. In these situations, the most clinically useful tool for growth assessment becomes tracking the child’s height percentile on the CDC growth charts at cdc.gov over time, which identifies the child’s actual growth trajectory and compares it to the US population rather than to parental genetics. Children who track consistently at a given percentile (for example, consistently at the 30th percentile) are generally growing appropriately regardless of where their parents’ heights fall, while children who are falling across percentiles (their percentile declining on sequential measurements) warrant evaluation regardless of parental height data availability. The CDC growth chart monitoring tool and the American Academy of Pediatrics growth guidance at aap.org support this alternative tracking approach for children where parental height data is unavailable or unreliable.

Yes, the mid-parent height formula used in this calculator is the same calculation that US pediatricians refer to as the target height or genetic potential height calculation. The formula is taught in US medical schools and residency programs and is routinely applied during pediatric well-child visits when parents ask about their child’s likely adult height or when growth concerns arise. The standard clinical application uses the same formula presented here: (father’s height + mother’s height + 5 inches) / 2 for boys, and (father’s height + mother’s height – 5 inches) / 2 for girls, both expressed in inches. The 95% prediction range of plus or minus 4 inches is the clinically established accuracy bound for this method. Some pediatricians and growth specialists prefer to quote the range in centimeters (the formula in centimeters adds or subtracts 13 cm for sex rather than 5 inches, since 5 inches is approximately 12.7 cm), but the underlying calculation and accuracy are the same. The American Academy of Pediatrics clinical guidelines reference the mid-parent height formula as a standard part of growth assessment during pediatric primary care, and it is also used by pediatric endocrinologists as a screening reference when evaluating patients for growth hormone deficiency, constitutional delay of growth and puberty, and other conditions that may cause deviation from predicted height trajectory. The target height calculation is noted in the Nelson Textbook of Pediatrics, the standard US pediatric medicine reference text, and in the AAP’s Bright Futures guidelines for preventive pediatric care at brightfutures.aap.org.

The CDC growth charts, available at cdc.gov/growthcharts, are standardized reference charts that plot height, weight, and BMI against age and sex for US children from birth to age 20, showing where a child falls relative to the population in percentile terms. A child at the 50th percentile for height is taller than 50% of children of the same age and sex in the US; a child at the 75th percentile is taller than 75%. The charts were last updated in 2000 based on nationally representative US data and are the primary tool used by US pediatricians to monitor growth at well-child visits. The key clinical use of growth charts for height assessment is not a single measurement but the pattern of measurements over time: children normally track along a given percentile (for example, consistently at the 40th percentile) through childhood and adolescence, and this consistent tracking confirms appropriate growth even if the percentile appears low in isolation. What concerns pediatricians is a change in percentile trajectory, called crossing percentile lines, where a child who was at the 60th percentile at age 3 drops to the 20th percentile by age 6 without an explanation such as illness, stress, or a major change in nutrition. This crossing of percentile lines suggests the growth rate (height velocity in cm per year) has slowed below what is normal for the child’s age, prompting further evaluation. The CDC growth charts are used alongside the mid-parent target height to determine whether a child appears to be on track to reach their genetic height potential: a child at the 25th percentile whose parents’ mid-parent prediction corresponds to the 25th percentile is growing appropriately, while a child at the 25th percentile whose parental prediction suggests the 75th percentile has a significant growth deficit that warrants investigation.

Tall birth length is a weak predictor of tall adult height, though it is less reliable than parent heights because fetal growth is heavily influenced by maternal uterine environment, nutritional status, and placental function in addition to genetic factors. Babies who are long at birth are somewhat more likely to be tall adults than average-birth-length babies, but the correlation is relatively modest. The more predictive relationship between early childhood height and adult height develops gradually; by age 2, a child’s height has a correlation of approximately 0.7 with their adult height (meaning about 49% of adult height variation is explained by 2-year-old height), and by age 4, this correlation increases to approximately 0.8. By ages 7 to 8, a child’s current height and its percentile on the CDC growth chart has become a reasonably good predictor of adult height, assuming continued healthy growth without significant illness or nutritional disruption. One important caveat: children who are early maturing (entering puberty early) may be tall for their age during mid-childhood (10-12) compared to their peers who have not yet started puberty, but they typically end at a shorter adult height than their mid-childhood ranking would suggest because their growth plates close earlier. Conversely, late-maturing children may appear shorter than peers during adolescence but continue growing longer and often end near or above the mid-parent prediction. For this reason, comparing a child’s height to the mid-parent prediction is more meaningful than comparing to peers during puberty, when the timing of the pubertal growth spurt creates wide apparent variation that does not reflect final adult height ranking.

While genetics is the dominant determinant of adult height, accounting for approximately 60 to 80% of the variation in height between individuals based on twin and family studies, several non-genetic factors can meaningfully push a child’s actual height above or below their genetic potential as estimated by the mid-parent formula. The most significant modifiable factors in the US context are: nutrition throughout childhood and adolescence, particularly adequate protein, calcium, vitamin D, zinc, and iron intake during the key growth periods of infancy (birth to 2 years), early childhood (2-6 years), and the pubertal growth spurt (approximately ages 10-14 for girls, 12-16 for boys); chronic illness, particularly conditions affecting nutrient absorption (celiac disease, inflammatory bowel disease, cystic fibrosis), oxygen delivery (severe asthma, congenital heart disease), or metabolism; sleep quality and duration, since growth hormone secretion is concentrated during slow-wave sleep and chronically poor sleep can suppress growth velocity; physical activity, which has a modest positive effect on growth hormone secretion and bone health; stress, including severe chronic psychosocial stress, which is associated with psychosocial short stature (also called stress-related growth failure or deprivation dwarfism), a rare but real phenomenon in children experiencing severe chronic emotional neglect or abuse; and altitude and geographic factors, which have small effects on height through oxygen availability and other mechanisms studied in high-altitude populations. For most US children with access to adequate nutrition and healthcare, these factors will not prevent achievement of genetic height potential, and the mid-parent formula provides a reasonable estimate of expected adult height. The USDA nutrition guidelines at dietaryguidelines.gov and the American Academy of Pediatrics nutrition guidance at aap.org outline the specific nutritional needs across childhood that support optimal growth.

The Khamis-Roche method, developed by Harry Khamis and Alex Roche in 1994, is an alternative adult height prediction method that incorporates the child’s current height, current weight, current age, and both parents’ heights into a statistical prediction model. Unlike the mid-parent formula which uses only parental heights, the Khamis-Roche method uses the child’s own growth status at the time of measurement as an additional predictor, which makes it more accurate than the mid-parent formula alone for children ages 4 to 17.5 years who have existing height measurements available. The reported accuracy of the Khamis-Roche method is approximately plus or minus 2.1 inches for the 90% prediction interval (compared to plus or minus 4 inches for the 95% mid-parent interval), making it meaningfully more precise for individual height prediction when the child’s current data is available. The Khamis-Roche method requires lookup tables with sex-specific regression coefficients for each age group that are somewhat complex to apply manually, which is why this calculator uses the simpler mid-parent formula as a starting point. Pediatric endocrinologists and pediatric growth specialists typically use the Khamis-Roche or similar sophisticated methods for clinical height prediction when a more precise estimate is needed. The original Khamis-Roche study was published in the journal Pediatrics and is referenced in the American Academy of Pediatrics growth assessment resources at aap.org. For most parents seeking a general estimate of their child’s likely adult height, the mid-parent formula provides a useful and clinically validated starting point that can be confirmed with more detailed assessment through the child’s pediatrician if more precision is desired.

Bone age assessment, which uses an X-ray of the left hand and wrist to estimate skeletal maturity relative to chronological age, is one of the most useful tools for refining adult height predictions beyond what the mid-parent formula alone can provide. The growth plates (epiphyseal plates) visible on the wrist X-ray have a characteristic appearance that changes as they mature from open cartilage (actively growing) to narrowing and eventually closed (fused, indicating growth is complete). A pediatric radiologist reads the bone age by comparing the child’s growth plate appearance to standard reference images from the Greulich-Pyle atlas or using the more detailed Tanner-Whitehouse scoring method, producing an estimated skeletal age in years and months. A child with a bone age of 9 years but a chronological age of 11 years has a bone age that is 2 years younger than their chronological age, suggesting they have approximately 2 additional years of growth remaining compared to an average child of that chronological age. This information, combined with the current height, growth velocity, and mid-parent prediction, allows a pediatric endocrinologist to generate a more refined adult height prediction. The Bayley-Pinneau tables, published as part of the Greulich-Pyle atlas, allow direct calculation of predicted adult height from current height and bone age in children whose bone age is known. Bone age X-rays are typically ordered by a pediatrician or pediatric endocrinologist when there is clinical concern about a growth abnormality, unusually early or late puberty, or significant deviation from expected growth trajectory. The radiation exposure from a single hand X-ray is minimal and well below clinical concern thresholds. The Pediatric Endocrine Society at pedsendo.org and the Society for Pediatric Radiology at pedrad.org provide clinical guidance on the appropriate use of bone age assessment in pediatric growth evaluation.

Yes, both scenarios are possible due to the nature of polygenic height inheritance and the prediction interval around any parental height estimate. The mid-parent formula generates a point prediction, but the actual range of heights that children of two tall parents might reach spans approximately 8 inches at the 95% confidence level (the mid-parent prediction plus or minus 4 inches). This means two parents who are both 6 feet tall (predicted child height approximately 6’1″ for a boy) could have a son who ends up at 5’9″ (4 inches below prediction) with no medical explanation; this simply reflects the natural genetic variation in which combinations of height-influencing genes the child inherits. Even tall parents who both carry mostly tall-enhancing genetic variants will occasionally produce children who inherit a disproportionate number of the other parent’s shorter-height variants, leading to a child who is shorter than both parents. The reverse (short parents with a tall child) is also possible through the same mechanism, though it occurs less often at the extremes because very short parents have fewer tall-height genetic variants available to pass on. From a medical perspective, a child who is significantly shorter than would be expected from their parents (more than 4 to 5 inches below the mid-parent prediction) warrants a pediatric evaluation to rule out medical causes of growth deviation, including growth hormone deficiency, thyroid disorders, or skeletal dysplasias. However, some children who are shorter than their parental prediction simply inherited an unusual combination of shorter-height variants from both parents rather than having a medical cause. The distinction is made through clinical assessment including growth velocity analysis, bone age, and laboratory testing as indicated, typically ordered through the child’s pediatrician or a referral to a pediatric endocrinologist.

Yes, the mid-parent height formula can be applied before a child is born to estimate their likely adult height based on the two biological parents’ heights, which is the same calculation this tool performs. Pre-birth use of the formula is particularly useful for expectant parents who are curious about their future child’s likely height, and the calculation produces the same result regardless of whether it is applied during pregnancy or after birth, since the inputs (parental heights) do not change. The application of the mid-parent formula before birth is sometimes discussed during preconception counseling or genetic counseling consultations, particularly when one or both parents have a known growth condition or are significantly outside the normal height range (very short stature suggesting a genetic or endocrine condition, or very tall stature which in rare cases is associated with conditions like Marfan syndrome or Klinefelter syndrome). It is important to note that the formula’s accuracy and the plus or minus 4-inch prediction interval apply the same way for pre-birth use as for post-birth use; the formula produces the same central estimate and the same uncertainty range, and it does not become more or less accurate because the child has not yet been born. What does improve prediction accuracy as a child grows is incorporating the child’s own current height and bone age, which are obviously not available pre-birth. For parents of unborn children or newborns, the mid-parent formula is the best available height prediction tool; as the child grows through early childhood (age 4-5), the prediction can be refined by also tracking the child’s actual growth percentile on the CDC charts relative to the parental prediction.

The 5-inch sex adjustment in the mid-parent height formula (added for boys, subtracted for girls) exists to correct for the well-documented average height difference between adult US men and women. When two parents of different sexes have their heights averaged directly without any correction, the result reflects the average of a male and female height, which is intermediate between typical male and female adult heights. This unadjusted average would systematically overestimate girls’ heights and underestimate boys’ heights because it fails to account for the sex-linked biological factors that make men on average taller than women. The 5-inch adjustment (applied as half the approximately 10-inch average difference between US male and female height) corrects for this sex-based difference by shifting the prediction appropriately for the expected sex of the child. The mechanism behind the male-female average height difference involves multiple biological factors including the longer duration of male adolescent growth (boys start puberty later and grow for longer before growth plate closure), the higher peak growth hormone secretion and IGF-1 levels in adolescent males, and sex chromosome effects on bone growth programming. The Y chromosome and its gene complement, along with testosterone’s role in bone growth during puberty, contribute to the taller average male height seen consistently across virtually all human populations worldwide, with the specific magnitude of the difference (approximately 5 to 6 inches in the US) reflecting both genetic and environmental factors. The sex correction in the mid-parent formula was established through population studies and is validated in the Tanner height prediction framework referenced in pediatric growth textbooks including Nelson’s Textbook of Pediatrics. The CDC growth charts at cdc.gov have separate charts for boys and girls precisely because of these well-established sex differences in growth patterns, timing, and final adult height distribution.

The mid-parent height formula as used in this calculator does not apply any race- or ethnicity-specific correction factors; it applies the same formula to all children regardless of parental racial or ethnic background. This is the standard approach used in US clinical pediatric practice, where the same formula is used across all patient populations with the understanding that the prediction accuracy may be slightly lower for children of parents from populations with very different average heights than the US average. The formula implicitly assumes that the sex adjustment of 5 inches applies universally, but the actual male-female height difference varies somewhat across racial and ethnic groups (it is approximately 4.5 to 5 inches in some Asian populations and somewhat larger in some Northern European populations). For most clinical purposes in the US, these population-level differences in the sex adjustment are smaller than the 4-inch prediction interval of the formula and do not meaningfully change the practical clinical utility of the prediction. The CDC growth charts at cdc.gov, which are used alongside the mid-parent prediction in US pediatric practice, are based on a racially and ethnically diverse US sample that reflects the contemporary US child population, providing a relevant population reference for comparing a child’s growth regardless of racial or ethnic background. Some international growth chart sets and research applications do apply population-specific height norms for countries or ethnic groups where average heights differ substantially from US norms. For US children of diverse backgrounds, the standard CDC growth charts and the mid-parent formula as applied in this calculator are the appropriate reference tools as endorsed by the American Academy of Pediatrics at aap.org and the CDC at cdc.gov.

Short stature in children is clinically defined as height below the 3rd percentile for age and sex on the CDC growth charts (approximately 2 standard deviations below mean height), but this threshold alone does not determine whether medical evaluation is needed, since approximately 3% of all healthy children are in this range by statistical definition. The clinical distinction between short stature that is a normal variant versus short stature that reflects an underlying medical condition is made by analyzing the pattern and context of the growth, not just the height percentile at a single measurement. Patterns that suggest normal variant short stature and do not require extensive medical workup include: familial short stature (child is short but growing at a normal rate and tracks along a consistent percentile, and parental heights explain the child’s height through the mid-parent prediction); constitutional delay of growth and puberty (child is short and pubertal development is delayed, but bone age is also delayed and corresponds to the child’s growth stage, and family history often shows a similar pattern of delayed but ultimately normal growth); and short stature without other symptoms in a child who is growing at a normal velocity along a consistent CDC percentile. Patterns that prompt medical evaluation and possible referral to a pediatric endocrinologist include: growth velocity that is consistently below normal for age (less than 5 cm per year in children ages 4 to 9, or less than expected for pubertal stage during adolescence), which means the child is falling farther from their expected percentile rather than tracking along it; height significantly below what the mid-parent prediction would predict without an identified cause; short stature accompanied by other symptoms such as weight gain without increased food intake (thyroid dysfunction), fatigue, excessive thirst or urination (diabetes), abdominal symptoms (celiac disease), or dysmorphic features suggesting a genetic syndrome; or any height below the 1st percentile (more than 2.5 standard deviations below mean). The Pediatric Endocrine Society at pedsendo.org, the American Academy of Pediatrics at aap.org, and the MAGIC Foundation at magicfoundation.org (a US patient advocacy organization for children with growth disorders) all provide family-accessible resources for understanding when short stature warrants medical evaluation and what the evaluation process involves.