Guide

How Accurate Are Height Predictors, Really?

By the GoTaller team · Published July 14, 2026

The honest answer up front: a good height predictor gives you a range with a center, and the range is the honest part. The center comes from real science — growth references plus your parents' heights — and most people do land within a few inches of it. But no method, app, or doctor's formula can tell you exactly how tall you'll be, and none can tell you when you'll stop growing. Anyone quoting pinpoint accuracy is describing their marketing, not their math.

Ask Reddit and you'll get the other extreme: "as real as astrology and magic crystals," as one r/tall commenter put it. That's overcorrecting. Height prediction sits in between — it's statistics, and statistics done openly is useful. Here's what each method can actually deliver, so you can calibrate how much to trust any number you're given (including ours — we make a height prediction app, and this page describes exactly what our own tools can and can't do).

The methods, ranked by evidence

Bone age (Greulich-Pyle / Bayley-Pinneau) — the clinical gold standard

An X-ray of the hand and wrist, read against skeletal-maturity references, tells a clinician how much growing your bones have left — which is the question every other method can only approximate from age. This is the most accurate approach that exists, and no app can do it, because no app can X-ray you. If you need a real answer for a medical reason, this is the one; it's a pediatrician or endocrinologist conversation.

Khamis-Roche — the published statistical method

A peer-reviewed method (published in Pediatrics, 1994) that predicts adult height from a child's age, sex, current height and weight, and the parents' heights — no X-ray needed. Its defining virtue is honesty: it was published with its error bands, which span several centimeters and narrow as a child approaches maturity. Reddit's more careful commenters cite it by name for a reason. If a calculator tells you its Khamis-Roche estimate is "within about 2 in (5 cm) for most kids," that's the method working as designed — the window is the accuracy.

Mid-parental height (Tanner) — the classic formula

Add your parents' heights, add 5.1 in (13 cm) for a boy or subtract it for a girl, divide by two. That's the whole formula — clinicians have used it for decades as a "target height" anchor. It's genuinely informative (genetics is the biggest single factor in adult height) and genuinely limited: it knows nothing about you — your current height, your growth so far — so by itself it's a family average, not a personal forecast. Best used, as we use it, blended with a growth-reference projection.

Growth-reference percentile projection (WHO/CDC) — the curve-following method

Take your exact age, sex and current height; find your percentile on a reference population (WHO or CDC growth charts); project forward assuming you roughly hold your curve. This is how pediatric growth tracking actually works, and it's the backbone of our calculator — combined with the mid-parental anchor, with the uncertainty band widening the younger you are and when a parent's height is unknown. Its known weakness is the assumption itself: kids who shift percentile lanes during puberty (early and late bloomers) are exactly the ones it serves worst — which is why the band exists.

Web calculators — same math, easier to judge

The height calculators on big reference sites run the same published methods above — usually Khamis-Roche or mid-parental — and the good ones say so. That's the useful habit to build as a reader: the question is never "app or website?", it's "which method, and does it show its work?" A web calculator that names its formula beats an app that doesn't, and an app that names its formula beats both a mystery website and a mystery app. Two practical checks before trusting any of them: does the result come with a range (single exact numbers are a red flag), and does it ask for your sex and exact age (a predictor that doesn't can't be using growth references at all)?

"AI" prediction — unrankable

Most paid predictor apps describe their method with one word: AI. No formula, no training data description, no validation study, no error range — which means there is nothing to rank. Unpublished isn't automatically wrong, but it's unfalsifiable, and in a market where six of eight apps paywall the result, "trust us, it's AI" is doing sales work, not science work. A black box asking for a subscription deserves more skepticism than a formula you can check, not less.

Why "98.5% accurate" claims don't hold up

One popular app's marketing site claims its predictions are "98.5% Accurate." Here's the problem — not with the number, but with the sentence: accuracy of a height prediction is meaningless until you define the tolerance. 98.5% of predictions within what — half an inch? Two inches? Any tolerance wide enough makes any predictor "98.5% accurate"; predicted-to-the-centimeter would be impossible for every method on this page, including the clinical ones. With no published tolerance, cohort, or study, the figure can't be checked — and unfalsifiable precision is the oldest trick in wellness marketing. The credible presentations run the other way: published methods advertise their error bands. The window is the accuracy.

What no predictor can tell you

When you'll stop growing. Growth-plate closure tracks puberty stage, not birthdays, and varies by years between individuals. This is the single most-asked question and the one no formula answers well.
Whether you're a late bloomer. A 15-year-old who hasn't hit their growth spurt and a 15-year-old who finished theirs can be the same height today and end up 6 in (15 cm) apart. Age-based methods can't fully separate them — bone age can, which is why it's the clinical standard.
Anything medical. Falling across percentile lines, a growth spurt that never seems to arrive, or heights far outside the family pattern are doctor questions. A predictor is for curiosity and planning, never for diagnosis.
How to beat the estimate. Sleep, nutrition and posture help you reach your trajectory — and posture work can reclaim 1–3 cm (about ½–1 in) of slouched height at any age — but nothing an app sells lengthens bones after growth plates close. Any product implying otherwise is the reason this article exists.

Can ChatGPT predict your height?

People genuinely ask it — "how tall will I be?" is now a ChatGPT prompt. What happens under the hood: the model recalls the same public formulas described above (usually mid-parental) and does the arithmetic in text, sometimes correctly. It has no data advantage over a calculator — no growth-reference tables indexed to your exact age and sex, no percentile context, no consistent uncertainty band, and a nonzero rate of plain arithmetic slips. If you want the mid-parental number, a purpose-built tool that shows its formula is the same math with fewer failure modes. (It's a fine use of ChatGPT to explain the methods, though. This page tries to beat it at that too.)

Try the transparent version

Everything above is why our tools work the way they do. The adult-height calculator combines a WHO growth-reference projection with the mid-parental anchor and shows a range that widens the younger you are — it will tell you "growth nearly complete" rather than invent centimeters that aren't coming. The height comparison tool gives your percentile for your exact age and sex. The child height predictor runs the same math in parent language, with the Tanner formula printed on the page. All three are free, run in your browser, store nothing, and document their formulas — so you don't have to trust us, you can check us.

FAQ

What is the most accurate height prediction method?

Bone-age assessment — an X-ray of the hand read against skeletal maturity references — is the clinical gold standard, and only a doctor can do it. Among the methods an app or calculator can run, Khamis-Roche and growth-reference percentile projection are published, validated approaches; both produce a range of several centimeters, not an exact number. Any method claiming pinpoint accuracy is overselling.

Are parent-height calculators accurate?

The mid-parental (Tanner) formula gives a genuinely useful center point — most children end up within a few inches of it — but on its own it ignores your current height and how far along you are, which is why calculators that combine it with a growth-reference projection do better. Treat the mid-parental number as the middle of a range, not a destination.

Can a height predictor tell me when I'll stop growing?

No. Timing is the one thing no formula does well: growth-plate closure varies by years between individuals and tracks puberty stage, not birthdays. A predictor can say roughly how much growth typically remains at your age; it cannot promise your personal timeline. Only a bone-age X-ray gets close, and that's a clinical call.

Is ChatGPT accurate at predicting height?

ChatGPT applies the same public formulas you'd find in any calculator — when it doesn't make arithmetic slips, which language models still do. It has no data advantage, no growth-reference tables loaded for your exact age and sex, and it won't consistently show its uncertainty. A purpose-built calculator with a documented formula is the more reliable way to run the same math.