Bone Age Estimation Calculator

Bone age (skeletal age) is how mature a child’s skeleton is, compared against their actual age in years. Pediatricians use it to work out how much growing is left and to tell apart causes of short or tall stature that look identical on a growth chart.

Read this before you read the number below

Bone age is measured from an X-ray of the left hand and wrist, read against a standard atlas (the Greulich-Pyle method) or scored bone by bone (Tanner-Whitehouse). What the radiologist is looking at is the growth plates: how far the cartilage has been replaced by bone, and which small bones of the wrist have appeared and fused yet.

Height cannot substitute for that X-ray, and this page cannot either. The estimate below is a rough inference from height-for-age, and it will be wrong for exactly the children who most need a real answer. Two examples that a height-based guess gets backwards:

• A short child with familial short stature (short parents) usually has a bone age that matches their years exactly. There is nothing to find, and they will be a short adult.
• A short child with constitutional delay of growth and puberty (the classic “late bloomer”) has a bone age one to three years behind, and a good deal of growing left.

Both are short. Both look the same on a growth chart. Only the X-ray separates them, and the answer changes what happens next. The same applies at the tall end, where advanced bone age can be an early sign of precocious puberty or a hormonal disorder.

So treat this page as a height-for-age comparison with a crude maturity hint attached, and treat the adult height prediction as a conversation starter rather than a forecast.

The height-for-age inference, and its limits:

• A child well above average height for their age often has a somewhat advanced bone age
• A child well below average may have a delayed bone age, or may simply have short parents
• Around the average the inference tells you almost nothing at all

Average heights by age (approximate midpoints):

Key concepts:

• Advanced bone age: the skeleton is maturing faster than the calendar. Growth plates will close sooner, so there is less growing left than the child’s age suggests.
• Delayed bone age: the skeleton is running behind. Plates close later, so more growth remains. This is the good news finding in a short child.
• A gap of up to about 1 year in either direction is within normal variation and is not, on its own, a reason to do anything.

Predicted adult height here follows the Bayley-Pinneau idea: current height divided by the fraction of adult height a child has typically reached at a given skeletal maturity. Bayley-Pinneau is designed to take a radiological bone age. Feeding it an inferred one, as this page must, adds a great deal of slack, and the honest error bar is several centimetres in each direction. Real clinical use also has the child’s mid-parental height alongside it, which this page does not ask for.

When to actually see someone

Height percentile alone is a poor trigger. What pediatric endocrinologists watch for is:

• Crossing percentile lines downward after age 3, which matters far more than being at a low percentile and staying there
• Growth of less than about 5 cm a year between age 4 and puberty
• A big mismatch with the parents, either direction
• Signs of puberty before 8 in girls or 9 in boys, or none by 13 and 14 respectively

A child who is at the 5th percentile and tracking steadily along it is usually fine. A child who slides from the 50th to the 15th over two years is worth investigating even though they are still nearer average.

Important: This is an educational estimate. A genuine bone age requires an X-ray read by a trained physician, and any real concern about a child’s growth belongs with a pediatrician who can plot the actual curve.