Type in two heights, pick a sex, and any mid-parental height calculator will hand you a confident-looking number. What most of them won't tell you is that the formula behind it explains only about a third of why kids end up the height they do. Here's the calculator, the real formula, and — more usefully — an honest read on what the number can and can't tell you.
What Is Mid-Parental Height?
Mid-parental height (MPH) is a simple genetic estimate of a child's adult height, based entirely on the two biological parents' heights. It was developed in 1970 by British researchers James Tanner, Herbert Goldstein, and R.H. Whitehouse as a way to build parent-aware growth charts, so a short child with two short parents wouldn't be flagged the same way as a short child with two tall parents.
The formula adjusts for the average height difference between men and women — about 13 cm — before averaging the two parents:
Boys: (Father's height + Mother's height + 13 cm) ÷ 2
Girls: (Father's height + Mother's height – 13 cm) ÷ 2
The result is treated as the center of a range, not a single predicted number. Tanner's original work put that range at ±8.5 cm — meaning roughly 94% of children (the 3rd to 97th percentile) end up somewhere inside mid-parental height plus or minus 8.5 cm. In later work, Tanner refined this slightly to ±9 cm for girls and ±10 cm for boys, though the simpler ±8.5 cm figure is what most calculators — including the one above — still use for simplicity.
How to Use the Calculator
How Accurate Is This, Really?
This is the part most calculator pages skip entirely, and it matters more than the formula itself. A 2024 study published in the journal Children tracked height data across 23 very large families — an average of 11 adult children each — and compared their actual adult heights to what the standard Tanner formula predicted.
The results were more humbling than most parents expect: mid-parental height explained only 36% of the variation in children's final adult height, even though the underlying heritability of height itself is around 74%. On average, children ended up 2.7 cm taller than their mid-parental height predicted — largely because each generation has trended taller than the one before it, an effect the original 1970 formula has no way to account for.
Why "regression to the mean" matters: Children of very tall parents tend to land a bit shorter than the simple average predicts, and children of very short parents tend to land a bit taller. This is a well-known statistical pattern, not a flaw in any one family — extreme parental heights partly reflect random genetic luck that doesn't fully pass down. A simple average overcorrects for both ends.
Population and Era Matter Too
The original formula was built from British children measured in the 1960s. Height has risen across most populations since then — a pattern demographers call the "secular trend" — and the formula was never updated to account for it. A comprehensive 2025 review pulled together studies testing Tanner's formula outside its original British population and found it consistently underestimates adult height elsewhere: by roughly 2.3 cm in Taiwanese children, similarly in Korean and Asian Indian cohorts, and by as much as 4–6 cm in one small Spanish cohort. In every case, the gap ran in the same direction — real children ended up taller than the 1970 formula predicted.
Better Options When More Precision Matters
| Method | Typical Accuracy | What It Adds |
|---|---|---|
| Mid-parental height | ±8.5–10 cm | Just two parent heights — fast, but explains only about a third of the real variation |
| Khamis-Roche method | ±4–6 cm | Adds the child's own current height, weight, and age — no X-ray needed, more accurate than MPH alone |
| Bone age (Bayley-Pinneau / TW methods) | ±3–5 cm | Uses a hand-and-wrist X-ray to estimate skeletal maturity — the clinical gold standard, especially for early or late maturers |
None of these require a specialist visit to try informally — except bone age, which does require an X-ray and a clinician to interpret it. If a family genuinely needs a precise prediction (for a suspected growth disorder, for instance), a pediatric endocrinologist is the right next step, not a more elaborate home calculation.
What This Number Can (and Can't) Tell You
The practical takeaway: Use mid-parental height as one rough data point, not the final word. A child tracking well outside the ±8.5 cm range — especially combined with a slowing growth rate — is a better reason to talk to a pediatrician than the single MPH number by itself. Genetics sets a wide lane, not a fixed line.
Frequently Asked Questions
Is mid-parental height the same as target height?
Yes, these terms are used interchangeably in most clinical literature. "Mid-parental height" refers to the calculation itself, while "target height" usually refers to that number plus its ±8.5 to ±10 cm range — the full expected band, not just the midpoint.
Why does the formula add or subtract 13 cm?
13 cm approximates the average adult height difference between men and women. Adding it to a girl's mid-parental calculation (or subtracting it for boys, depending on which version you use) puts both parents' heights on the same sex-adjusted scale before averaging. It's worth noting this is a fixed constant rather than a percentage — a detail that later researchers have flagged as one of the formula's simplifications.
My child is already outside the predicted range — should I worry?
Not automatically. Given that the formula explains only about a third of real height variation, being somewhat outside the range is common and not inherently a red flag. What matters more is whether your child's own growth rate and percentile tracking are stable over time — see our guide on telling if a child is growing normally for the more reliable signals to watch.
Does this work for adopted children or if I don't know a biological parent's height?
No — mid-parental height is a genetic estimate, so it requires biological parent heights to mean anything. If one or both biological parents' heights are unknown, this calculation isn't applicable, and growth should be assessed using standard percentile tracking instead.
