BYTETOOLS

Child Height Predictor

Predict a child's adult height with the mid-parental method from both parents' heights, with a realistic range and the double-height-at-two cross-check.

Optional cross-check

The old paediatric rule of thumb is that a child’s height at age two is about half their adult height. It is a rough cross-check on the mid-parental figure, not a second opinion — it typically lands within about 10 cm for boys and is less reliable for girls, whose growth pattern peaks earlier.

Predicted adult height

178.0 cm

Most children finish within 169.5 cm to 186.5 cm — that spread of roughly ±8.5 cm is what the mid-parental method can honestly promise, and it is wide on purpose.

178.0 cm
Target height
169.5 cm
Lower end
186.5 cm
Upper end
—
Double at age 2

How it is worked out

(178.0 cm + 13 cm + 165.0 cm) ÷ 2 = 178.0 cm

The mid-parental method averages the two parents after shifting one of them by 13 cm, which is roughly the average adult height difference between men and women. Height is strongly heritable — parents explain most of the variation between children — but nutrition, general health, sleep, puberty timing and plain chance fill in the rest, which is where the ±8.5 cm comes from.

A rough population estimate, not a growth assessment and not medical advice. It cannot account for growth conditions, early or late puberty, chronic illness, or a child who has been consistently under or over their expected percentile. If you are worried about how a child is growing, a paediatrician plotting real measurements on a growth chart — and, where needed, a bone-age X-ray — will tell you far more than any formula. Everything is calculated in your browser and nothing is uploaded.

What is the Child Height Predictor?

The mid-parental method predicts adult height as (father's height + mother's height + 13 cm for a boy, or − 13 cm for a girl) ÷ 2. Most children finish within about 8.5 cm either side of that target.

  • Mid-parental target height with the standard 13 cm sex correction
  • ±8.5 cm expected range shown as prominently as the point estimate
  • Optional double-the-height-at-age-two cross-check
  • Centimetres or feet and inches, with results shown in both
  • Full working displayed so you can check the arithmetic
  • Calculated entirely in your browser — no measurements are uploaded

How to use the Child Height Predictor

  1. 1

    Choose centimetres or feet and inches, then select whether the child is a boy or a girl.

  2. 2

    Enter the father's height and the mother's height.

  3. 3

    Read the predicted adult height and the range around it.

  4. 4

    Optionally switch on the height-at-age-two cross-check and enter that measurement.

  5. 5

    Compare the two estimates in the working panel — a large gap usually just means the child tracks a different percentile from their parents.

About the Child Height Predictor

The ByteTools Child Height Predictor uses the mid-parental method that paediatricians reach for first: average the two parents' heights after shifting one of them by 13 cm, which is roughly the average adult height difference between men and women. Add 13 cm for a boy, subtract it for a girl.

Just as important as the number is the range around it. The tool reports a ±8.5 cm target range, which is about two standard deviations and is genuinely wide — that spread is the honest limit of what parental heights can tell you. There is also an optional cross-check using the old rule that a child's height at age two is roughly half their adult height, so you can see whether the two rough methods agree.

Heights can be entered in centimetres or in feet and inches, and results are shown in both. Everything runs in your browser and nothing is uploaded. This is a population estimate, not a growth assessment and not medical advice.

Frequently asked questions

How do you calculate a child's predicted adult height?

Add both parents' heights, add 13 cm for a boy or subtract 13 cm for a girl, then divide by two. For a 180 cm father and a 165 cm mother that gives 179 cm for a son and 166 cm for a daughter. The realistic range is about 8.5 cm either side.

How accurate is the mid-parental height method?

It gets the middle of the range right for most children but the range itself is wide — roughly ±8.5 cm covers about 95% of outcomes. Parental height explains most of the variation between children, but nutrition, illness, sleep, puberty timing and ordinary chance fill in the rest.

Is it true that a child's height at age two is half their adult height?

It is a rough rule of thumb, most often quoted for boys, and it typically lands within about 10 cm. Girls develop earlier, so for them the same rule is often applied at 18 months instead. Treat it as a cross-check rather than a second opinion.

Why is the predicted range so wide?

Because a genuinely honest prediction has to be. Two standard deviations of adult height is around 8.5 cm either side of the target, and a narrower number would be false precision. A child at the top of their range and a child at the bottom are both entirely normal.

Can a child grow taller than both parents?

Yes, and it happens often. Height is influenced by many genes plus environment, so children regularly land outside the parental average in both directions — better childhood nutrition and health alone have pushed average heights up across generations.

When should I speak to a doctor about my child's height?

If a child's growth crosses percentile lines on their chart, if they are much shorter or taller than the mid-parental range predicts, or if growth slows or stops unexpectedly. A paediatrician plotting real measurements over time — and, where needed, checking bone age — tells you far more than any formula.

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