For adults aged 18 to 64, a healthy BMI is 18.5 to 24.9 at every age. Over 65, NICE advises reading BMI with caution, as a slightly higher BMI (roughly 23 to 28) may be protective. For children aged 2 to 17, BMI is compared with others of the same age and sex using centiles: the 2nd to 91st centile is a healthy weight.
Adult BMI chart by age
The NHS and NICE use the same BMI categories for every adult from 18 upwards. What changes with age is how much weight you tend to carry around your middle and how much muscle you have, so the way a BMI should be read changes a little.
| Age | Underweight | Healthy BMI | Overweight | Obesity | Notes |
|---|---|---|---|---|---|
| 18–24 | < 18.5 | 18.5 – 24.9 | 25 – 29.9 | 30+ | Same adult categories |
| 25–34 | < 18.5 | 18.5 – 24.9 | 25 – 29.9 | 30+ | Weight often starts to creep up |
| 35–44 | < 18.5 | 18.5 – 24.9 | 25 – 29.9 | 30+ | Muscle loss begins; check waist |
| 45–54 | < 18.5 | 18.5 – 24.9 | 25 – 29.9 | 30+ | Menopause can shift fat to the waist |
| 55–64 | < 18.5 | 18.5 – 24.9 | 25 – 29.9 | 30+ | NHS Health Check offered from 40 |
| 65+ | < 18.5 (take care below 23) | ≈ 23 – 28 often lowest risk | Read with caution | 30+ | Avoid unplanned weight loss |
For South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean adults: healthy 18.5–22.9, overweight 23–27.4, obesity 27.5+ at all adult ages (NICE NG246).
Why the average BMI rises with age. In England, the share of adults who are overweight or living with obesity is lowest among 16 to 24 year olds and highest in middle age (Health Survey for England 2022). That is the average, not a target – the healthy range stays the same.
BMI after 65
Getting older brings natural loss of muscle and bone. A small reserve of weight can help older people recover from illness and protects against frailty and falls. NICE’s 2025 obesity guideline (NG246) says BMI should be interpreted with caution in people aged 65 and over, taking into account other health conditions and the possible protective effect of a slightly higher BMI.
- If you are over 65 and your BMI is under about 23, it is worth checking that you are eating enough protein and energy. See the NHS advice on keeping your weight up in later life.
- Unplanned weight loss – for example losing 5% of your weight in 3 to 6 months without trying – should always be checked by a GP.
- If your BMI is 30 or more, losing weight can still help your joints, blood pressure and blood sugar, but it should be planned with your GP so you keep your muscle.
BMI chart for girls aged 2 to 18
Children’s BMI naturally changes as they grow, so the NHS compares a child’s BMI with other children of the same age and sex. The values below are the BMI at the key centile lines for girls.
| Age | Underweight (≤2nd) | Healthy weight (2nd–91st) | Overweight (91st–98th) | Very overweight (≥98th) |
|---|---|---|---|---|
| 2 years | ≤ 13.0 | 13.0 – 17.4 | 17.4 – 18.5 | ≥ 18.5 |
| 3 years | ≤ 13.0 | 13.0 – 17.3 | 17.3 – 18.5 | ≥ 18.5 |
| 4 years | ≤ 13.3 | 13.3 – 17.8 | 17.8 – 19.1 | ≥ 19.1 |
| 5 years | ≤ 13.0 | 13.0 – 17.7 | 17.7 – 19.3 | ≥ 19.3 |
| 6 years | ≤ 12.9 | 12.9 – 18.0 | 18.0 – 19.7 | ≥ 19.7 |
| 7 years | ≤ 12.9 | 12.9 – 18.4 | 18.4 – 20.4 | ≥ 20.4 |
| 8 years | ≤ 13.0 | 13.0 – 19.0 | 19.0 – 21.3 | ≥ 21.3 |
| 9 years | ≤ 13.2 | 13.2 – 19.7 | 19.7 – 22.2 | ≥ 22.2 |
| 10 years | ≤ 13.5 | 13.5 – 20.4 | 20.4 – 23.2 | ≥ 23.2 |
| 11 years | ≤ 13.9 | 13.9 – 21.2 | 21.2 – 24.1 | ≥ 24.1 |
| 12 years | ≤ 14.4 | 14.4 – 22.0 | 22.0 – 25.1 | ≥ 25.1 |
| 13 years | ≤ 14.9 | 14.9 – 22.8 | 22.8 – 26.0 | ≥ 26.0 |
| 14 years | ≤ 15.4 | 15.4 – 23.6 | 23.6 – 26.8 | ≥ 26.8 |
| 15 years | ≤ 15.9 | 15.9 – 24.2 | 24.2 – 27.5 | ≥ 27.5 |
| 16 years | ≤ 16.3 | 16.3 – 24.8 | 24.8 – 28.0 | ≥ 28.0 |
| 17 years | ≤ 16.6 | 16.6 – 25.2 | 25.2 – 28.5 | ≥ 28.5 |
| 18 years | ≤ 16.9 | 16.9 – 25.6 | 25.6 – 28.9 | ≥ 28.9 |
BMI values (kg/m²) at each centile on the UK90 reference, at the child’s birthday. Thresholds used by the NHS for individual children.
BMI chart for boys aged 2 to 18
| Age | Underweight (≤2nd) | Healthy weight (2nd–91st) | Overweight (91st–98th) | Very overweight (≥98th) |
|---|---|---|---|---|
| 2 years | ≤ 13.5 | 13.5 – 17.5 | 17.5 – 18.6 | ≥ 18.6 |
| 3 years | ≤ 13.3 | 13.3 – 17.4 | 17.4 – 18.4 | ≥ 18.4 |
| 4 years | ≤ 13.6 | 13.6 – 17.6 | 17.6 – 18.8 | ≥ 18.8 |
| 5 years | ≤ 13.5 | 13.5 – 17.4 | 17.4 – 18.7 | ≥ 18.7 |
| 6 years | ≤ 13.3 | 13.3 – 17.5 | 17.5 – 18.9 | ≥ 18.9 |
| 7 years | ≤ 13.3 | 13.3 – 17.8 | 17.8 – 19.5 | ≥ 19.5 |
| 8 years | ≤ 13.3 | 13.3 – 18.3 | 18.3 – 20.2 | ≥ 20.2 |
| 9 years | ≤ 13.4 | 13.4 – 18.8 | 18.8 – 21.0 | ≥ 21.0 |
| 10 years | ≤ 13.6 | 13.6 – 19.5 | 19.5 – 21.9 | ≥ 21.9 |
| 11 years | ≤ 13.9 | 13.9 – 20.2 | 20.2 – 22.8 | ≥ 22.8 |
| 12 years | ≤ 14.3 | 14.3 – 20.9 | 20.9 – 23.7 | ≥ 23.7 |
| 13 years | ≤ 14.8 | 14.8 – 21.6 | 21.6 – 24.6 | ≥ 24.6 |
| 14 years | ≤ 15.3 | 15.3 – 22.4 | 22.4 – 25.4 | ≥ 25.4 |
| 15 years | ≤ 15.8 | 15.8 – 23.2 | 23.2 – 26.2 | ≥ 26.2 |
| 16 years | ≤ 16.3 | 16.3 – 23.9 | 23.9 – 27.0 | ≥ 27.0 |
| 17 years | ≤ 16.7 | 16.7 – 24.5 | 24.5 – 27.7 | ≥ 27.7 |
| 18 years | ≤ 17.2 | 17.2 – 25.1 | 25.1 – 28.3 | ≥ 28.3 |
BMI values (kg/m²) at each centile on the UK90 reference, at the child’s birthday. Thresholds used by the NHS for individual children.
To check a child at their exact age (in years and months), use the child BMI calculator. It plots the result on a UK-WHO centile chart.
How the NHS describes a child’s BMI
2nd centile or below
Underweight. A GP or health visitor may want to check growth and diet.
2nd to 91st centile
Healthy weight for their age, sex and height.
91st to 98th centile
Overweight. Small changes for the whole family usually help most.
98th centile or above
Very overweight. Speak to your GP, school nurse or health visitor for support.
Children should never be put on a weight loss diet without advice from a health professional. In most cases the aim is to slow weight gain so they grow into a healthier weight. Read child growth centiles explained.
Frequently asked questions
Does a healthy BMI change with age?
For adults aged 18 to 64 the healthy BMI range is the same: 18.5 to 24.9. Over 65, a slightly higher BMI of around 23 to 28 is often linked with the lowest risk. Children use age- and sex-specific centiles instead of fixed numbers.
What is a healthy BMI for a 60 year old?
A healthy BMI for a 60 year old is 18.5 to 24.9, the same as for younger adults. Waist size becomes more important from middle age, so aim for a waist less than half your height.
What is a normal BMI for a 13 year old?
It depends on sex. For a 13 year old girl, a healthy BMI is roughly 14.9 to 22.8; for a 13 year old boy roughly 14.8 to 21.6 (2nd to 91st centile). Use the child BMI calculator for an exact centile.
Why do children have lower BMIs than adults?
Body fat changes a lot during childhood. BMI typically falls from about age 1 to 6, then rises through puberty. That is why a single cut-off like 25 cannot be used for children.
What BMI is too low for an older person?
There is no single cut-off, but in later life a BMI below about 23 may mean a person has less reserve to cope with illness. A BMI under 18.5 is underweight at any age. Unplanned weight loss should always be checked by a GP.
Related tools and guides
About this page
How this guide works
Adult ranges come from NICE NG246 and the NHS BMI tool. Child values are the BMI at the 2nd, 91st and 98th centiles of the UK90 reference (reanalysed 2009), which is used on UK-WHO charts from age 4, with WHO standards below 4. The NHS uses these centiles to describe a child’s weight.
Sources
Medical disclaimer: this guide is general information for adults and is not a diagnosis or medical advice. bmicalculatornhs.net is independent and not affiliated with the NHS. Speak to your GP, pharmacist or another qualified health professional about your own health. Full disclaimer.