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MasterMath

Child Adult Height Predictor

A child's estimated adult height from their parents', using the mid-parental method. It comes with a margin of plus or minus eight and a half centimetres, which is what makes the figure honest.

Estimated adult height

—

Estimated adult height—
95 % range—
Average of the parents—
Correction for sex—
In feet and inches—
Width of the range—

How this was worked out

    Indicative result. This is a statistical reference, not a prediction. Growth is monitored with percentile charts and interpreted by a paediatrician.

    The formula

    Boy: (father + mother) / 2 + 6.5 · Girl: (father + mother) / 2 − 6.5

    Where it comes from

    The mid-parental method averages both parents' heights and adds or subtracts 6.5 centimetres by sex, which is half the thirteen centimetres separating average adult male and female height. Height is highly heritable — around 80 % of the variation is genetic — but the rest is not nothing: nutrition, sleep and childhood illness move the outcome within that margin.

    How to work it out by hand

    1. Add the father's height to the mother's
    2. Divide by two
    3. Add 6.5 cm for a boy, subtract them for a girl
    4. The realistic margin is ±8.5 cm around that figure

    What is worth knowing

    The ±8.5 cm margin is not decoration: around 95 % of cases fall inside it, and without it the central figure looks like a prediction when it is a reference. Seventeen centimetres of range is a lot, and that is precisely the information. If a child clearly departs from their growth channel on the percentile charts, or if the mid-parental figure does not match what is actually happening, that is worth a consultation, not a two-line calculation.

    Frequently asked questions

    How much can you trust it?

    95 % of cases fall within ±8.5 cm. That is seventeen centimetres of range: the central figure is a reference, not a forecast.

    Where do the 6.5 centimetres come from?

    Half of the thirteen centimetres separating average adult male and female height.

    Is height decided purely by genetics?

    About 80 % of the variation, yes. The rest is moved by nutrition, sleep and childhood illness.

    Does it work if one parent is much taller?

    The method averages, so it works the same. What it cannot capture is which part each child inherits.

    When should I see a paediatrician?

    If the child departs from their percentile channel, if yearly growth is very low, or if the mid-parental figure does not match what you see.