Published by MetaSys Limited · Page updated · Editorial policy. Educational information; not a medical review.
How the Mid-Parental Height Method Works
Parents ask me some version of this question constantly: "how tall is my kid going to be?" It's a natural curiosity — you're watching a toddler or a grade-schooler grow and wondering where the trajectory ends. The mid-parental height method is the simplest, most widely cited way to get a reasonable estimate, and it only needs one piece of information from each parent: their height.
The Formula Behind the Estimate
This calculator uses the classic mid-parental height formula, sometimes referred to as the Khamis-Roche simplified approach, which has been used by pediatricians for decades as a quick reference point. For boys, you add the mother's height in centimeters to the father's height in centimeters, add 13, and divide by two. For girls, the calculation is identical except you subtract 13 instead of adding it before dividing. That 13 cm adjustment exists because adult men are, on average, about 13 cm taller than adult women, so the formula shifts the combined parental average up or down depending on the child's sex before landing on a same-sex target.
The result isn't a single guaranteed number — it's a midpoint estimate. Height is influenced by dozens of genes plus environmental factors, so real children don't all land exactly on their calculated mid-parental height. That's why this tool also shows a typical expected range of about ±8.5 cm (roughly ±3.3 inches) around the estimate. Statistically, most children — around two-thirds — end up within that range of their calculated value, which is a useful way to think about the "normal" spread rather than treating the point estimate as destiny.
How to Use This Result Practically
I'd treat this number as a rough compass, not a GPS pin. It's genuinely useful for a few practical purposes: setting expectations with family members, giving a pediatrician a data point to compare against a child's actual growth curve, or simply satisfying curiosity about whether your child is tracking "on target" relative to family genetics. If a doctor is tracking your child's height-for-age percentile over time, the mid-parental estimate can serve as a helpful cross-check — if your child's growth curve is consistently far outside the expected range in either direction, that's often when a pediatrician might look more closely at nutrition, hormonal factors, or bone age.
One thing I always tell parents: don't over-interpret small differences. A child predicted at 175 cm who ends up at 172 cm or 178 cm hasn't defied genetics — that's well within the normal range this formula anticipates. The prediction is most useful in aggregate, across large groups of children, which is exactly the context it was originally developed and validated in.
Important Caveats to Keep in Mind
This method has real limitations worth understanding. It only accounts for the two parents' heights — it can't capture the influence of grandparents, other relatives, or specific genetic variants tied to height. It also can't account for anything that happens after conception: nutrition quality throughout childhood, chronic illness, sleep, physical activity, and hormonal health can all shift a child's actual adult height away from this genetic baseline. Puberty timing matters too — children who start puberty earlier or later than average sometimes end up outside the expected mid-parental range simply due to timing rather than any underlying issue.
Because of all this, I'd encourage using this calculator for general context and conversation-starting purposes, not as a medical prediction. If you have real concerns about your child's growth — whether they seem to be growing unusually slowly, quickly, or inconsistently — a pediatrician can run proper growth-chart tracking and, if needed, bone age assessments that go well beyond what a simple formula like this can offer.
Read Methodology & Sources and Calculator Limitations. Report an error.