Obesity Index Chart: BMI Categories From Healthy Weight to Severe Obesity

An obesity index chart is a quick way to understand how adult body mass index, or BMI, is divided into healthy weight, overweight and different obesity categories.

For most adults in the UK, the current NICE classification is straightforward:

• BMI 18.5 to 24.9 kg/m² = healthy weight
• BMI 25 to 29.9 kg/m² = overweight
• BMI 30 to 34.9 kg/m² = obesity class 1
• BMI 35 to 39.9 kg/m² = obesity class 2
• BMI 40 kg/m² or above = obesity class 3.

That chart is useful, but it should not be treated as a complete assessment of someone's health.BMI is calculated from height and weight. It does not directly distinguish:body fat, muscle, bone or where body fat is stored.NICE therefore recommends interpreting BMI in context and, for adults with BMI below 35 kg/m², using waist-to-height ratio as an additional estimate of central adiposity. This page provides both the standard UK obesity chart and the practical information needed to interpret it correctly.

Key things to know

The standard NICE BMI chart applies to most adults.

It is not designed to be copied directly onto:children, young people, or pregnancy.

Children and young people need age-adjusted BMI centile charts rather than the fixed adult BMI categories. NICE's current obesity guideline also specifically states that its adult obesity-management guidance does not cover pregnancy.

BMI thresholds also need adjustment when interpreting risk in some ethnic backgrounds.

So the correct way to use an obesity chart is:

calculate BMI

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find the relevant adult category

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consider whether adjusted thresholds apply

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consider waist-to-height ratio where appropriate

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interpret the result within the wider health context.

UK Body Mass Index Obesity Index Chart

The current NICE adult classification is:

NICE uses these classifications for adults unless the person is in one of the ethnic groups for whom lower thresholds are recommended.

What Does Each BMI Category Mean?

A BMI chart is easier to use when you understand what each section represents, because that helps you interpret a bmi result rather than just locate a number on the chart.

Below BMI 18.5

This is the Underweight category and falls below the standard NICE healthy-weight range.

A BMI below 18.5 falls below the standard NICE healthy-weight range and may warrant further assessment depending on the person's circumstances.The chart should not be interpreted as saying lower is always healthier.BMI has a lower as well as an upper healthy-weight boundary.

BMI 18.5 to 24.9

This is the standard adult healthy-weight category, or normal weight in standard weight categories.

However, NICE advises using clinical judgement because someone within this range may still have increased central adiposity.

A healthy-range BMI therefore does not automatically mean abdominal fat distribution or cardiometabolic risk is ideal.

BMI 25 to 29.9

This is the standard overweight category.

It is below the BMI 30 threshold used for obesity in most adults.

The overweight range is associated with a higher risk of high blood pressure and other health risks.

BMI 30 to 34.9

This is obesity class 1.

A high BMI in this range is associated with higher risk of developing health problems, including heart disease, and obese individuals also have a higher risk of certain cancers.

BMI 30 is therefore the standard point at which the general adult chart moves from overweight to obesity.

BMI 35 to 39.9

This is obesity class 2.

BMI 35 is clinically relevant because several specialist weight-management and treatment pathways also use BMI alongside weight-related health conditions when assessing eligibility.

BMI 40 or Above

This is obesity class 3.

Older charts may label this range differently. Current NICE guidance uses the term:

obesity class 3.

What Is a BMI Obesity Chart?

A BMI obesity chart visually links a person's: height with body weight to estimate BMI.

BMI itself is calculated using: weight in kilograms ÷ height in metres².

For example, someone who is 1.70 metres tall and weighs 86.7 kg has a BMI of approximately 30.0 kg/m².

That places them at the beginning of obesity class 1 under the standard NICE adult chart.

The important point is that the weight corresponding to BMI 30 changes with height.

BMI estimates total body fat only roughly and can be less accurate in taller adults with larger frames, so ideal weight should not be treated as a single fixed number.

There is no single body weight that means “obesity” for every adult.

Obesity Chart by Height and Weight

The following table shows the approximate body weight at which each major BMI boundary begins for selected adult heights.

These values are calculated directly from the BMI formula and are rounded to the nearest 0.1 kg.

The column headed “BMI 30 starts at” shows the approximate weight at which standard obesity class 1 begins for someone of that height.

The table is an aid rather than a substitute for calculating the person's exact BMI.

How Do I Use the Obesity Chart?

Use three steps.

Step 1: Measure Your Height

Use an accurate height measurement without shoes where possible.

Step 2: Measure Your Weight

Use a reasonably consistent scale.

For tracking over time, weigh under similar conditions each time rather than comparing a morning measurement with one taken after a large evening meal.

Step 3: Match Height and Weight

Use the table to see where your weight falls relative to the major BMI thresholds.

For example: height = 175 cm, weight = 95 kg.At 175 cm. BMI 30 begins around 91.9 kg.BMI 35 begins around 107.2 kg.So 95 kg falls within:obesity class 1under the standard adult BMI classification.

For an exact value, use a bmi calculator or other calculator rather than relying only on the rounded lookup table.

How Do You Calculate BMI Yourself?

The formula is:BMI = weight in kg ÷ height in metres².

Example:height = 1.80 m, weight = 100 kg.First:1.80 × 1.80 = 3.24.Then:100 ÷ 3.24 = approximately 30.9.A BMI of 30.9 falls within:obesity class 1using the standard NICE adult ranges.

What BMI Is Classed as Obese?

For most adults:BMI 30 kg/m² or above.25 is the upper limit of the healthy range on the standard adult chart.

The classes are:

• 30–34.9 = class 1
• 35–39.9 = class 2
• 40+ = class 3.

However, that is not the correct threshold for every ethnic background.

This is where many simple obesity charts become incomplete.

Why Does NICE Use Lower BMI Thresholds for Some Ethnic Backgrounds?

NICE states that adults from South Asian, Chinese, other Asian, Middle Eastern ethnic backgrounds. Black African and African-Caribbean backgrounds are more prone to central adiposity and can develop cardiometabolic risk at lower BMI values.

For these groups, NICE recommends using: BMI 23 to 27.4 = overweight, BMI 27.5 or above = obesity.NICE also advises that classes 2 and 3 are usually identified by reducing the standard thresholds by:2.5 kg/m².

Adjusted BMI Obesity Chart for These Groups

The practical NICE framework is approximately:

NICE's committee explains that reducing the general class 2 and class 3 boundaries by around 2.5 kg/m² gives approximately:

32.5 kg/m² for class 2

and

37.5 kg/m² for class 3.

This is an important correction to charts that show only BMI 30 as the point at which obesity becomes relevant for everyone.

Does the BMI Chart Differ for Men and Women?

The standard NICE adult BMI categories are not separated into different charts for men and women.For most adults, the same standard ranges apply.However, BMI does not show differences in body composition or fat distribution.This is one reason additional measurements can sometimes be useful.

For adults with BMI below 35 kg/m², NICE recommends waist-to-height ratio as an additional estimate of central adiposity for both sexes.

What Is Waist-to-Height Ratio?

Waist-to-height ratio compares waist circumference with height. Use the same units for both.

For example: waist = 85 cm, height = 170 cm. 85 ÷ 170 = 0.50.

NICE classifies waist-to-height ratio as:

These categories can be used for adults with BMI below 35 kg/m² across sexes and ethnicities.

What Is the “Half Your Height” Rule?

NICE gives a particularly simple message for waist-to-height ratio:

try to keep your waist measurement below half your height.

For example:

• height = 180 cm.
• Half of height = 90 cm.
• A waist below:90 cm

would correspond to a waist-to-height ratio below 0.5.

This does not replace BMI, but it can add useful information about abdominal fat distribution when BMI is below 35.

Why Is Waist-to-Height Ratio Not Routinely Added Above BMI 35?

NICE recommends the additional waist-to-height assessment specifically for adults with BMI below:

35 kg/m².

NICE recommends using waist-to-height ratio alongside BMI for adults with a BMI below 35 kg/m². Above this BMI, the NICE classification does not recommend routinely adding waist-to-height ratio to the assessment.

This means someone at BMI 40 does not need a higher waist measurement to “prove” that BMI class 3 applies.

BMI already determines the standard classification.

Can a Healthy BMI Still Hide Central Adiposity?

Yes.

NICE explicitly advises using clinical judgement when interpreting the healthy-weight BMI category because someone within it may still have central adiposity.

This is one reason a simple green section on a BMI chart should not be interpreted as a guarantee of low cardiometabolic risk.

Waist distribution can provide additional context.

Can BMI Put a Muscular Person in the Obesity Range?

Yes.BMI cannot tell whether body weight comes mainly from fat, muscle, or another tissue.

NICE therefore advises interpreting BMI cautiously in adults with high muscle mass because it may be a less accurate estimate of adiposity in these people.

For example, a muscular athlete could have BMI above 30 without having the same body-fat profile as someone else with the identical BMI.

Are Body-Fat Scales Better Than a BMI Chart?

Not necessarily.Home body-fat scales commonly use bioimpedance, but their readings should not be treated as a definitive measurement of body fat.

NICE advises against using bioimpedance as a substitute for BMI as a practical measure of general adiposity in adults.

A home body-fat reading may provide additional information, but it should not automatically replace BMI or clinical assessment.

Does Age Change the BMI Chart?

For adults aged 65 and over, NICE recommends interpreting BMI cautiously, and interpretation can differ at different ages even though the chart itself stays the same.

The assessment should consider existing health conditions, functional capacity and the possible protective effect of a slightly higher BMI in some older people.

The standard chart may still be calculated, but the result should not be interpreted without context.

Can Children Use This Obesity Chart?

No.This is an adult BMI chart.Children and young people are still growing, so fixed adult boundaries such as BMI 25, BMI 30, BMI 35, cannot simply be applied.

NICE recommends using charts adjusted for age and sex,with BMI centiles used to classify overweight, clinical obesity and severe obesity in children and young people.

Current NICE clinical thresholds include:overweight at the 91st BMI centileclinical obesity at the 98th centilesevere obesity at the 99.6th centile.

Can This Adult BMI Chart Be Used During Pregnancy?

This adult BMI chart should not be used as though ordinary adult weight-management classification applies unchanged during pregnancy.

NICE has separate guidance covering nutrition and weight management during pregnancy, so pregnancy requires a different clinical context.

What Does “Morbidly Obese Chart” Mean?

Some older charts use the term “morbidly obese” for BMI 40 kg/m² or above.

Current NICE terminology uses: obesity class 3.

So if an older “morbidly obese chart” shows: BMI 40+ the modern UK equivalent is obesity class 3.

The BMI boundary has not changed simply because the preferred terminology has changed.

Is BMI 40 the Highest Obesity Category?

Under the standard NICE adult classification, class 3 begins at BMI 40.There is no separate standard NICE class 4 category above it. Therefore BMI 40, BMI 45, BMI 50 and higher values remain within obesity class 3.This does not mean all these BMI values carry identical individual health circumstances.It only means they fall within the same standard BMI classification.

Can an Obesity Chart Tell Me My Health Risk?

Only partly.BMI provides useful information about general adiposity at a population level, but it does not measure an individual's complete health profile.NICE recommends considering other factors such as central adiposity, existing health conditions, medical history, ethnicity and muscle mass.

For adults with BMI below 35 kg/m², higher waist-to-height ratios are associated with increased risk of:type 2 diabeteshypertensionand cardiovascular disease.

A BMI chart should therefore be used as a starting point for assessing health risks and supporting prevention rather than as a diagnostic tool.

Does Moving From BMI 29.9 to 30 Suddenly Change Health?

No.BMI categories are practical boundaries.Biological risk does not suddenly transform the moment BMI moves from 29.9 to 30.0.

The category changes from overweight to obesity class 1, but health risk exists along a continuum.

That is why NICE advises interpreting measurements alongside the person's wider circumstances rather than treating each cut-off as an absolute biological dividing line.

Can Someone Be Healthy With BMI Above 30?

BMI above 30 establishes a standard obesity classification for most adults, but it does not tell you which health conditions someone currently has.

One person may have normal blood pressure, good mobility and no diagnosed metabolic problem.Another person with the same BMI may have increased central adiposity, high blood pressure or abnormal blood glucose.The BMI classification can be the same while the wider health picture differs.

Should You Use an Obesity Chart to Choose Weight-Loss Medication?

No.BMI can form part of medicine eligibility, but a chart alone cannot determine whether prescription treatment is appropriate.Current NICE obesity-management pathways consider factors including BMI, weight-related comorbidities, treatment setting, and individual clinical circumstances.

A prescription decision also requires medical-history and safety assessment.The chart can identify a BMI category.It cannot prescribe treatment.

Should You Try to Reach the Healthy BMI Range as Quickly as Possible?

No.An obesity chart is a classification tool, not a target timetable.

Moving from a higher BMI towards a lower range can be useful when clinically appropriate, but the quickest possible change is not automatically the safest or most sustainable approach.

Weight-management goals should take account of nutrition,physical activity, medical conditions and long-term maintenance. A chart should help explain where someone starts, not encourage extreme short-term dieting.

How Often Should BMI Be Checked?

There is no need to calculate BMI every day.

Height usually changes very little in most adults, so BMI movement is mainly driven by changes in body weight.

If someone is following a weight-management plan, tracking the longer-term weight trend is generally more useful than recalculating BMI after every small fluctuation.

BMI categories are broad.

Daily changes rarely alter the clinical picture meaningfully.

What if My BMI Is Close to a Category Boundary?

Treat the number as part of a range rather than as a pass-or-fail result.

For example BMI 29.8 and BMI 30.1are extremely close biologically even though they appear on different sides of the standard classification boundary.

Focus on the overall trend waist measurement where appropriate health indicators and sustainable behaviours.

The classification helps organise care but should not create unnecessary anxiety over tiny differences.

When Should You Discuss BMI With a Healthcare Professional?

A clinical discussion may be useful if:

• BMI falls within a higher obesity class
• BMI is low or there are underweight concerns
• waist-to-height ratio indicates increased central adiposity
• weight has changed substantially without explanation
• weight-related conditions are present
• mobility or sleep is being affected
• previous attempts at weight management have not been sustainable
• prescription treatment is being considered.

NICE recommends assessing comorbidities and other factors that may affect or be affected by weight rather than considering BMI alone. Professional medical advice is important when BMI findings need to be interpreted in context.

Obesity Index Chart: Key Takeaway

The UK obesity index chart provides a straightforward way to classify adult BMI.

For most adults:

• 18.5–24.9 kg/m² = healthy weight
• 25–29.9 kg/m² = overweight
• 30–34.9 kg/m² = obesity class 1
• 35–39.9 kg/m² = obesity class 2
• 40 kg/m² or above = obesity class 3.

The chart becomes more useful when height is added.

For example, obesity class 1 begins at approximately:

• 67.5 kg for someone 150 cm tall
• 76.8 kg at 160 cm
• 86.7 kg at 170 cm
• 97.2 kg at 180 cm
• 108.3 kg at 190 cm

Those values are not separate health targets. They simply show how the BMI 30 threshold changes with height.

BMI also has important limitations.It cannot directly tell how much body fat someone has, whether weight comes largely from muscle or where fat is distributed.NICE therefore recommends cautious interpretation in people with high muscle mass and in adults aged 65 and over. For adults with BMI below 35 kg/m², waist-to-height ratio adds useful information about central adiposity.

NICE classifies:

• 0.4–0.49 as healthy central adiposity
• 0.5–0.59 as increased central adiposity
• 0.6 or above as high central adiposity

with the simple recommendation to keep waist circumference below half of height.Another major limitation of generic obesity charts is ethnicity.

For adults from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds, NICE uses lower practical thresholds because cardiometabolic risk can occur at lower BMI levels.

For these groups:

• BMI 23–27.4 = overweight
• BMI 27.5 or above = obesity

with class 2 and class 3 thresholds usually reduced by approximately 2.5 kg/m² from the standard adult boundaries.

Finally, this is an adult chart.Children and young people require BMI centile charts adjusted for age and sex, while pregnancy has its own weight-management guidance.

Use the standard NICE adult BMI chart as the starting point, but do not treat the category as a complete measure of health. Check whether ethnicity-adjusted thresholds apply, consider waist-to-height ratio when BMI is below 35 kg/m², and interpret BMI carefully when muscle mass, age or other individual factors may make the number less informative.

Medical Disclaimer

This article provides general educational information about adult BMI and obesity classification in the UK. BMI is a practical screening and classification measure rather than a direct measurement of body fat or an individual diagnosis of overall health. Different thresholds may be appropriate for some ethnic backgrounds, and BMI requires cautious interpretation in people with high muscle mass and in older adults. Adult BMI charts should not be applied directly to children, young people or pregnancy. Anyone concerned about their BMI, waist measurement, unexplained weight change or weight-related health risk should seek appropriate advice from a qualified healthcare professional. This article is not a substitute for professional medical advice.