- October 3, 2026
Table of Contents
ToggleIf you are asking “Am I overweight?”, your Body Mass Index (BMI) can provide a useful starting point. BMI compares your weight with your height and is commonly used by the NHS to assess whether an adult is underweight, a healthy weight, overweight or living with obesity.
However, BMI is not a complete measure of health. It cannot distinguish between muscle and fat, and your ethnic background, waist measurement, age, medical conditions and other factors can affect how your result should be interpreted.
In 2026, the NHS continues to use BMI alongside other measurements, including waist-to-height ratio, to help assess weight-related health risks. For most adults, a BMI of 25 to 29.9 is classed as overweight, while a BMI of 30 or above is classed as obese. For people from certain ethnic backgrounds, including South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds, health risks can occur at lower BMI levels.
This guide explains how to calculate BMI, how to read an NHS BMI chart, what counts as overweight in the UK, why waist size matters, and what you can do if your BMI is above the recommended range.
Medical disclaimer: This article is for general health information and does not replace personalised advice from a GP, pharmacist, dietitian or other qualified healthcare professional.
BMI stands for Body Mass Index.
It is a calculation based on your:
The formula is:
BMI = weight (kg) ÷ height (m)²
For example, if someone weighs 70 kg and is 1.70 m tall:
70 ÷ (1.70 × 1.70) = BMI 24.2
The NHS uses BMI as one way of assessing whether an adult’s weight falls within a healthy range. Its adult BMI calculator is designed for people aged 18 and over.
To calculate your BMI manually:
Use kilograms (kg).
If your scales show stones and pounds, convert your weight into kilograms first.
Use metres.
For example:
For someone who is 1.70 m tall:
1.70 × 1.70 = 2.89
If the person weighs 70 kg:
70 ÷ 2.89 = 24.2
Their BMI is approximately 24.2.
The NHS calculator displays BMI to one decimal place and then provides a weight category.
For most adults, the NHS uses the following BMI categories:
| BMI | NHS category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0 or above | Obese |
These ranges apply to most adults.
A BMI below 18.5 falls into the underweight category.
Being underweight can sometimes indicate that you are not getting enough nutrition, although BMI alone cannot determine the reason for a person’s weight.
If you have unexpectedly lost weight, particularly without changing your diet or activity levels, speak to a GP. The NHS recommends medical advice for unexplained weight loss.
For most adults, this is considered the healthy-weight range.
However, having a BMI within this range does not automatically mean that every aspect of your health is healthy.
For example, you can have a healthy BMI while carrying excess fat around your waist.
This is why the NHS also recommends considering waist-to-height ratio in appropriate adults.
For most adults, a BMI between 25 and 29.9 is classed as overweight.
This does not mean that you are unhealthy simply because your BMI is above 25. BMI is a screening measurement rather than a diagnosis.
Your overall risk also depends on factors such as waist size, ethnicity, existing medical conditions and lifestyle.
For most adults, a BMI of 30 or higher is classed as obese.
The NHS explains that obesity is associated with an increased risk of several health conditions, including type 2 diabetes, heart disease, stroke, high blood pressure, some cancers, osteoarthritis and fatty liver disease.
According to the standard NHS BMI categories, a BMI of 25 to 29.9 is overweight for most adults.
But the word “overweight” should not be interpreted as a complete diagnosis of your health.
For example, a person with substantial muscle mass may have a high BMI despite having relatively little body fat. The NHS specifically warns that BMI cannot distinguish between muscle and fat.
Therefore, if your BMI is 25, 27 or 29, consider the result alongside other information rather than treating the number as a standalone health diagnosis.
One of the most important points in the current NHS guidance is that BMI thresholds can be different for some ethnic groups.
The NHS says people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds can have an increased risk of health problems at a lower BMI.
For these groups, the NHS uses:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–22.9 | Healthy weight |
| 23.0–27.4 | Overweight |
| 27.5 or above | Obese |
The NHS calculator asks about ethnic background because this can provide more appropriate advice about a person’s BMI result.
This is particularly relevant because metabolic health risks such as type 2 diabetes can occur at lower BMI levels in some ethnic groups.
BMI does not measure body fat distribution or metabolic risk directly.
Research and clinical guidance have shown that some populations can develop conditions such as type 2 diabetes and cardiovascular disease at lower BMI levels.
Therefore, using one BMI threshold for everyone can underestimate risk for some groups.
The NHS has incorporated ethnicity into its adult BMI calculator to provide more appropriate advice.
BMI is useful because it is simple, inexpensive and easy to calculate.
However, it has limitations.
BMI does not tell you:
For example, an athlete with considerable muscle mass could have a BMI above 25 without having excess body fat.
The NHS therefore recommends considering other measurements, including waist-to-height ratio where appropriate.
Carrying excess fat around the abdomen can increase health risks.
The NHS recommends that, where appropriate, you try to keep your waist measurement below half of your height.
For example, if you are:
170 cm tall
half of your height is:
85 cm
A waist measurement below 85 cm would meet the NHS’s general waist-to-height recommendation.
This measurement can provide additional information that BMI cannot.
To measure your waist:
The NHS waist-to-height calculator can be used alongside BMI to help assess whether you may be carrying too much fat around your abdomen.
The standard adult BMI categories are generally applied to both men and women.
However, BMI does not account for differences in body composition.
Two people with exactly the same BMI can have different:
This is another reason why BMI should be interpreted as part of a wider assessment.
BMI categories for adults are generally based on adult height and weight rather than having a separate standard BMI range for every age.
However, body composition changes as people age.
For example, muscle mass can decrease with age while body fat increases, even if body weight remains relatively stable.
This means BMI may not provide the full picture of health in older adults.
The NHS also identifies being over 55 as one factor that can make maintaining a healthy weight more difficult.
Weight gain happens when the body receives more energy from food and drink than it uses over time.
However, the reasons for weight gain are often more complicated than simply “eating too much”.
The NHS identifies several possible contributing factors, including:
This is why weight management should not be reduced to willpower alone.
Yes.
Depression can affect:
Some people lose weight when depressed, while others gain weight.
If you are experiencing low mood alongside weight changes, HealthCresto’s Depression vs Anxiety guide provides further information about common mental health symptoms.
You can also read our guide to depression symptoms in men and women.
Hormonal changes around menopause can affect body composition, appetite and where fat is stored.
The NHS lists menopause and perimenopause among factors that can make maintaining a healthy weight more difficult.
For more information, see HealthCresto’s guides on menopause symptoms in the UK and what age menopause starts in the UK.
Some medical conditions can make weight management more difficult.
The NHS lists conditions such as an underactive thyroid and Cushing’s syndrome among possible contributors.
If you have gained weight unexpectedly or are struggling to lose weight despite consistent lifestyle changes, speak with your GP.
A healthcare professional can consider your symptoms, medical history and medication rather than relying on BMI alone.
Some medicines can affect body weight.
The NHS identifies certain steroids, antidepressants and beta blockers among medicines that can contribute to weight gain.
This does not mean you should stop taking prescribed medication.
If you believe a medicine is affecting your weight, discuss it with your GP or pharmacist. They can determine whether the medication could be contributing and whether an alternative is appropriate.
Having excess body weight can increase the risk of several long-term health conditions.
According to the NHS, overweight and obesity are associated with increased risks of:
The relationship is not simply about BMI. Waist circumference, physical activity, diet, blood pressure, blood glucose and other factors also matter.
For related metabolic health information, see our guide to diabetes diet plans and foods to eat and avoid.
Yes.
Excess weight can increase the risk of high blood pressure and cardiovascular disease.
If you are concerned about your blood pressure as well as your weight, you can read HealthCresto’s guide to normal blood sugar levels.
Important: Blood sugar and blood pressure are different measurements. The linked article focuses on blood sugar levels, so speak to a healthcare professional if you are specifically concerned about blood pressure.
It can.
The NHS states that losing even 5% to 10% of body weight can improve health.
This means that weight management does not necessarily have to start with reaching an “ideal” BMI.
For some people, a relatively modest reduction can produce meaningful health benefits.
There is no universal answer.
Your appropriate target can depend on:
The NHS recommends speaking to a GP if your BMI is in the overweight or obese range and you want help losing weight, particularly if you also have conditions such as prediabetes, diabetes, high blood pressure, joint problems, high cholesterol, sleep apnoea or cardiovascular disease.
The NHS recommends combining healthier eating with increased physical activity.
Useful approaches include:
The NHS suggests aiming for approximately 0.5 to 1 kg (1 to 2 lb) per week when trying to lose weight.
For additional information, read HealthCresto’s guide on how many calories you should eat to lose weight.
There is no single calorie target that works for everyone.
Your calorie needs depend on factors including:
The NHS advises creating a calorie deficit by consuming fewer calories than your body uses, but the size of that deficit should be appropriate and sustainable.
Avoid extremely restrictive diets unless medically supervised.
Regular physical activity can support weight management and improve cardiovascular and metabolic health.
The NHS recommends adults aim for 150 minutes of moderate-intensity activity a week, which can be divided into smaller sessions.
Examples include:
Strength-based activity can also help maintain muscle mass.
If you have a medical condition, significant mobility limitations or have not exercised for a long time, discuss an appropriate activity level with a healthcare professional.
Walking can be an excellent way to increase physical activity.
It may help you:
The amount of weight you lose depends on your overall energy balance, diet, activity and individual circumstances.
You do not need to start with intense exercise. Gradually increasing daily movement can be a practical approach for many people.
Some people with obesity may qualify for prescription weight-management medicines.
Eligibility depends on the specific medicine, clinical circumstances and current NHS guidance.
HealthCresto has a dedicated guide explaining how to get weight-loss injections on the NHS.
You can also read our guide to Ozempic in the UK, including how it works, cost and NHS eligibility.
Do not buy weight-loss medicines from unregulated websites or use prescription medicines without appropriate medical supervision.
The standard NHS adult BMI calculator should not be used during pregnancy.
Pregnancy changes body weight and composition in ways that make standard BMI interpretation inappropriate.
If you are pregnant and concerned about your weight, speak with your midwife, GP or maternity team.
No.
The adult NHS BMI calculator is intended for people aged 18 and over. Children and teenagers aged 2 to 17 should use the NHS child and teenager BMI calculator, which considers age and sex as part of the assessment.
The NHS advises against using the adult calculator if you:
If you are concerned about your weight and have an eating disorder or think you may have one, seek professional support rather than focusing on BMI or calorie restriction.
You may want to speak with a GP if:
The NHS specifically recommends seeking GP advice for several of these circumstances.
If your BMI falls into the overweight range, don’t panic.
A sensible next step is to look at the bigger picture.
Consider:
This provides a more useful picture than BMI alone.
A healthy BMI does not necessarily mean you have no health risk.
You can have a BMI within the healthy range but still carry excess abdominal fat.
This is why the NHS recommends waist-to-height ratio as an additional measure for suitable adults.
Being overweight does not automatically mean that you currently have a health problem.
However, excess weight can increase the likelihood of developing certain long-term conditions over time.
Use your BMI result as a prompt to review your overall health rather than as a reason to panic or pursue rapid weight loss.
A GP or healthcare professional can help you understand your individual risk.
For most adults, yes. The NHS classifies BMI from 25 to 29.9 as overweight. However, BMI should be considered alongside factors such as ethnicity, waist measurement and muscle mass.
For most adults, yes. A BMI of 30 or above falls into the NHS obesity category.
For most adults, a BMI of 27 falls within the overweight range. For some ethnic groups, including South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean groups, the NHS uses lower BMI thresholds because health risks can occur at lower BMI levels.
For most adults, BMI 23 falls within the healthy-weight range. However, for certain ethnic groups, the NHS classifies BMI from 23 to 27.4 as overweight.
BMI is useful as a screening measure, but it is not a perfect measure of body fat or overall health. It cannot distinguish between muscle and fat.
For most adults, the NHS healthy BMI range is 18.5 to 24.9. Different thresholds apply to certain ethnic groups because health risks may occur at lower BMI levels.
For most adults, 25 to 29.9 is the overweight range. For certain ethnic groups, the NHS uses 23 to 27.4 as the overweight range.
No. BMI cannot distinguish muscle from fat. Someone with a high amount of muscle may have a BMI in the overweight or obese category despite having relatively low body fat.
Not necessarily based on BMI alone. Consider your waist measurement, ethnic background, health conditions, lifestyle and overall health. If you are concerned, discuss your result with a healthcare professional.
The NHS advises that you should try to keep your waist measurement below half your height.
Yes. Overweight and obesity are associated with an increased risk of type 2 diabetes.
The NHS recommends gradual weight loss and suggests aiming for around 0.5 to 1 kg per week rather than rapid weight loss.
Yes. The NHS provides weight-management advice, and some people may be eligible for additional clinical support depending on their BMI, health conditions and circumstances.
If you’re wondering “Am I overweight?”, your BMI is a useful place to start—but it shouldn’t be the only thing you look at.
For most adults in the UK:
For people from certain ethnic backgrounds, including South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds, the NHS uses lower BMI thresholds.
Your waist-to-height ratio, medical history, lifestyle, existing conditions and overall health can provide additional context.
If your BMI is above the healthy range, you do not need to make extreme changes overnight. The NHS recommends sustainable lifestyle changes, regular physical activity and gradual weight loss where appropriate. Even losing around 5% to 10% of body weight can provide health benefits.
For further weight-management information, explore HealthCresto’s weight-loss and calorie-counting resources, NHS weight-loss injection guide and Ozempic UK guide.
If you are worried about your weight, have unexplained weight changes, have an eating disorder, or have a condition that affects your weight, speak with your GP or another qualified healthcare professional rather than relying on BMI alone.
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