Does age change your BMI?
Age does not change the BMI number itself — it is always weight divided by height squared. Age changes how the number is interpreted:
- Ages 2 to 19: BMI is compared with other children of the same age and sex and reported as a percentile. That is why a BMI calculator with age is essential for children and teenagers.
- Ages 20 to about 65: the standard adult categories apply to everyone — 18.5–24.9 is healthy weight.
- 65 and over: the same categories are used, but many clinicians accept a BMI slightly above 25, because being underweight in later life is linked with frailty and poorer recovery from illness.
Average BMI rises with age
Adults typically gain weight slowly through their 30s, 40s and 50s while losing some muscle, so BMI tends to rise and body fat rises even faster. Two people with the same BMI at 25 and 65 often have very different amounts of muscle. That is one reason doctors look at waist size, blood pressure and blood tests rather than BMI alone.
BMI calculator in kg with age
Choose Metric to enter height in centimetres and weight in kilograms, or switch to US or UK units. Enter the age in whole years. For an exact children’s percentile including months, use the Child BMI Calculator.
Adult BMI categories at any age
| BMI (kg/m²) | Adult category (WHO) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40 or more | Obesity class III |
Healthy weight ranges by height
These ranges apply to adults of every age from 20 upwards:
| Height | BMI 18.5 | BMI 24.9 | BMI 30 |
|---|---|---|---|
| 150 cm | 41.6 kg | 56.0 kg | 67.5 kg |
| 155 cm | 44.4 kg | 59.8 kg | 72.1 kg |
| 160 cm | 47.4 kg | 63.7 kg | 76.8 kg |
| 165 cm | 50.4 kg | 67.8 kg | 81.7 kg |
| 170 cm | 53.5 kg | 72.0 kg | 86.7 kg |
| 175 cm | 56.7 kg | 76.3 kg | 91.9 kg |
| 180 cm | 59.9 kg | 80.7 kg | 97.2 kg |
| 185 cm | 63.3 kg | 85.2 kg | 102.7 kg |
| 190 cm | 66.8 kg | 89.9 kg | 108.3 kg |
| 195 cm | 70.3 kg | 94.7 kg | 114.1 kg |