Weight-for-age shows how heavy a child is compared with peers, but it does not account for height – a tall child will naturally be heavier. Use the BMI percentile calculator to judge weight relative to height.
How to use the Child Weight Percentile Calculator
- Sex
- Age
- Weight
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter sex, age and weight.
Tips
- Measure lying length for babies under 2 and standing height from age 2.
- Use the exact age in months for babies – a few weeks matters.
- Follow the trend across several visits; crossing two major percentile lines is more important than one value.
- Discuss concerns with your paediatrician.
Common mistakes to avoid
- Comparing a baby with the wrong sex chart.
- Reading the 50th percentile as “normal” and everything else as abnormal.
- Using corrected age incorrectly for premature babies.
Inputs explained
| Field | What to enter |
|---|---|
| Sex | Choose one: Male, Female |
| Age | Units: years, months |
| Weight | Units: kg, lb, st, g |
Example values
How the main result changes when Age changes and everything else stays at the example values above:
| Age (years) | Weight percentile (%) |
|---|---|
| 4 | 100 |
| 6 | 92 |
| 8 | 52 |
| 10 | 9 |
| 12 | 3e-1 |
| 16 | 6e-11 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
z = ((weight ÷ M)^L − 1) ÷ (L × S), with CDC weight-for-age LMS values
Percentile = Φ(z) × 100
Worked example
Inputs — Sex: Male; Age: 8 years; Weight: 26 kg.
Results — Weight-for-age z-score = 0.06; Weight percentile = 52 %; Percentile group = 50th–85th; Median weight for age = 25.8 kg.
Key terms
- Weight-for-age
- Weight compared with children of the same age and sex.
Frequently asked questions
What weight percentile is normal?
Between about the 3rd and 97th, especially if it matches the height percentile.
Why use BMI percentile instead?
BMI accounts for height, which weight-for-age does not.
How often should children be weighed?
At routine checks; frequent weighing at home is not needed.